Materials and Methods for Organic Light-Emitting Device Microcavity

ABSTRACT

The present teachings provide methods for forming organic layers for an organic light-emitting device (OLED) using a thermal printing process. The method can further use one or more additional processes, such as vacuum thermal evaporation (VTE), to create an OLED stack. OLED stack structures are also provided wherein at least one of the charge injection or charge transport layers is formed by a thermal printing method at a high deposition rate. The organic layer can be subject to post-deposition treatment such as baking. The structure of the organic layer can be amorphous, crystalline, porous, dense, smooth, rough, or a combination thereof, depending on deposition parameters and post-treatment conditions. The organic layer can improve light out-coupling efficiency of an OLED, increase conductivity, decrease index of refraction, and/or modify the emission chromaticity of an OLED. An OLED microcavity is also provided and can be formed by one of more of these methods.

RELATED APPLICATIONS

The present application is a non-provisional patent application andclaims the benefit of U.S. Provisional Patent Application No. 61/499,496filed on Jun. 21, 2011, which is incorporated herein in its entirety byreference.

FIELD

The present teachings relate to a process for forming layers of anorganic light-emitting device (OLED). The present teachings also relateto an OLED stack structure.

BACKGROUND

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. OLED technologies are reviewedin Geffroy et al., “Organic light-emitting diode (OLED) technology:material devices and display technologies,” Polym., Int., 55:572-582(2006). Several OLED materials and configurations are described in U.S.Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporatedherein by reference in their entirety.

In many cases, a large portion of light originating in an emissive layerwithin an OLED does not escape the device due to internal reflection atthe air interface, edge emission, dissipation within the emissive orother layers, waveguide effects within the emissive layer or otherlayers of the device (i.e., transporting layers, injection layers,etc.), and other effects. In a typical OLED, up to 50-60% of lightgenerated by the emissive layer can be trapped in a waveguide mode, andtherefore fail to exit the device. Additionally, up to 20-30% of lightemitted by the emissive material in a typical OLED can remain in a glassmode. The out-coupling efficiency of a typical OLED, thus, can be as lowas about 20%. See, for example, U.S. Patent Application Publication No.US 2008/0238310 A1, which is incorporated herein by reference in itsentirety.

Organic OLED layers, in a conventional process, are deposited by vacuumthermal evaporation (VTE). In such an OLED deposition process, organiclayers are usually deposited at a slow deposition rate (from 1Angstroms/second to 5 Angstroms/second) and the deposition time isundesirably long when a thick buffer layer is deposited. Moreover, tomodify the layer thickness, a stencil mask is usually applied to eithershield the vapor flux or allow it to pass through onto the substrate.Furthermore, the resulting organic layer usually has an index ofrefraction that is significantly higher than the index of refraction ofthe substrate glass. As such, some of the emitting light can be trappedin the organic layer and lost in a waveguide mode.

In vacuum thermal evaporation (VTE), a layer of hole transport material(HTM) is deposited in a vacuum at slow rate, for example, at about 0.2nm/sec for 110 nm at a total time of about 550 seconds or about 9.0minutes. No conventional technique, such as VTE, for forming organicthin films combines the large area patterning capabilities of inkjetprinting with the high uniformity, purity, and thickness controlachieved with vapor deposition. Given that inkjet-processed single layerOLED devices continue to have inadequate quality for widespreadcommercialization, and thermal evaporation remains impractical forscaling to large areas, it is desired to develop a technique that canoffer both high film quality and cost-effective large area scalability.

SUMMARY

According to various embodiments, the present teachings relate to adeposition method to rapidly form a buffer layer between alight-emitting layer (EML) and an electrode during the manufacture of anOLED stack. The method can provide an ultra-high deposition rate and apost deposition heat-treatment method can be used to reduce theroughness of the buffer layer. The thermal printing process providescapabilities to modify the organic layer's morphology, as well as itsnanostructure, microstructure, its electrical properties, and itsoptical properties, therefore leading to improved OLED performance. Themethods of the present teachings enable control of deposition conditionsand manipulation of buffer layer morphology, structure, and properties.For example, the method can provide a lowered charge injection barrier,a lowered index of refraction, an increased light out-couplingefficiency, and an increased the interface area at a recombination zonewhere electron or hole charges recombine and photons are generated.

According to various embodiments, the buffer layer can be formed that isporous, and it can be formed placed adjacent a transparent electrode.The buffer layer can exhibit a low index of refraction, comparable to asilica glass, and light extraction from the EML can be more efficient.In some embodiments, the buffer layer surface is made rough and morelight can be scattered or out-coupled into the transparent electrodelayer. In some embodiments, the buffer layer is made crystalline toincrease charge mobility, decrease voltage drop, and improve overallefficiency. In some embodiments, the buffer layer thickness is optimizedfor each color/wavelength to improve emission chromaticity and toachieve a microcavity effect. In some embodiments the buffer layer canbe used to improve an OLED color chromaticity.

According to various embodiments, the buffer layer can be made by amethod that combines a standard vacuum deposition technique (VTE) with athermal printing deposition technique. By changing the layer thickness,the emission spectrum can be tuned to optimize for a certain color orwavelength; for example for red, green, or blue. For example, the bufferlayer thickness can be made thickest for red, of intermediate thicknessfor green, and thinnest for blue. The method can be controlled such thata buffer layer printed at highly non-equilibrium rates can be made tohave areas of very distinct nanostructure (dense versus porous,amorphous versus crystalline, and smooth versus rough).

According to various embodiments, a method of forming a dried organiclayer for an organic light-emitting device is provided by the presentteachings. In some embodiments the method can comprise the steps ofapplying, energizing, transferring, and baking. A liquid ink for forminga layer of an organic light-emitting device can be applied to a transfersurface. The liquid ink can be defined by a carrier fluid and dissolvedor suspended film-forming organic material. The transfer surface can beenergized to substantially evaporate the carrier fluid and form a dryfilm organic material on the transfer surface. The dry film organicmaterial can be transferred from the transfer surface to a substratesuch that the dry film organic material is deposited on the substrate insubstantially a solid phase. Herein, such a process of applying,energizing, and transferring is referred to as thermal printing. Thermalprinting techniques and apparatuses that can be used include, forexample, those described in U.S. Patent Application Publications Nos. US2008/0311307 A1, US 2008/0308037 A1, US 2006/0115585 A1, US 2010/0188457A1, US 2011/0008541 A1, US 2010/0171780 A1, and US 2010/0201749 A1,which are incorporated herein in their entireties by reference. In someembodiments, the transfer surface can be positioned at a distance offrom about 1.0 μm to about 10.0 mm from the substrate during thetransferring, for example, at a distance of from about 10.0 μm to about100.0 μm from the substrate. The dry film organic material can bedeposited to build up a layer thickness at a rate of from about 0.1nm/sec to about 1.0 mm/sec, to form an organic layer on the substrate.In some embodiments the organic layer can be baked at a first baketemperature of from about 50° C. to about 250° C. for a first bake timeof from about 5.0 milliseconds to about 5.0 hours to form a first bakedorganic layer for an organic light-emitting device.

A method of forming a crystalline organic layer for an organiclight-emitting device is provided by the present teachings. The methodcan comprise an applying step, an energizing step, a transferring step,and a baking step. A liquid ink can be applied to a transfer surface forforming a layer of an organic light-emitting device. The liquid ink canbe defined by a carrier fluid and dissolved or suspended film-formingorganic material. The film-forming organic material can comprise amaterial that exhibits desired properties for a layer of an OLED. Thetransfer surface can be energized to substantially evaporate the carrierfluid and form a dry film organic material on the transfer surface. Thedry film organic material can have a glass transition range. The dryfilm organic material can be transferred from the transfer surface to asubstrate such that the dry film organic material is deposited on thesubstrate in substantially a solid phase. The transfer surface can bepositioned at a distance of from about 1.0 μm to about 10.0 mm from thesubstrate during the transferring, for example, at a distance of fromabout 10.0 μm to about 100.0 μm from the substrate. The dry film organicmaterial can be deposited to build up a layer thickness at a rate offrom about 0.1 nm/sec to about 1.0 mm/sec, to form a pre-bake organiclayer on the substrate. The pre-bake organic layer can be baked at abake temperature of from within the glass transition range to above theglass transition range to form a crystalline organic layer for anorganic light-emitting device. The crystalline organic layer can have aconductivity of from about 1.0×10⁻⁹ S/m to about 1.0×10⁻¹ S/m, forexample, from about 1.0×10⁻⁹ S/m to about 1.0×10⁻⁴ S/m, or from about1.0×10⁻⁹ S/m to about 1.0×10⁻⁷ S/m. Higher conductive HTM layermaterials can be used to achieve higher conductivities.

An organic light-emitting device is provided in accordance with thepresent teachings. The device can comprise a first electrode, acrystalline organic layer, an emitting layer, and a second electrode.The crystalline organic layer can be provided over and electricallyassociated with the first electrode and can have a conductivity of fromabout 1.0×10⁻⁹ S/m to about 1.0×10⁻⁷ S/m. The emitting layer can beprovided over and electrically associated with the crystalline organiclayer and can comprise a light-emitting organic material that emitslight at an emission wavelength. The second electrode can be providedover and electrically associated with the emitting layer such that theemitting layer is sandwiched between the first and second electrodes.

A method of decreasing the refractive index of an organic layer isprovided in accordance with the present teachings. The method cancomprise an applying step, an energizing step, and a transferring step,which together can be repeated for multiple applications of variousliquid inks, comprising respectively different dissolved or suspendedfilm-forming organic material. Each liquid ink can be applied to atransfer surface for forming a respective layer of an organiclight-emitting device. The transfer surface can be energized tosubstantially evaporate the carrier fluid and form a dry film organicmaterial on the transfer surface. The dry film organic material can betransferred from the transfer surface to a semi-transparent ortranslucent electrode disposed on a semi-transparent or translucentsubstrate such that the dry film organic material is deposited on thesemi-transparent or translucent electrode in substantially a solidphase. The transfer surface can be positioned at a distance of fromabout 1.0 μm to about 10.0 mm from the substrate during thetransferring, for example, at a distance of from about 10.0 μm to about100.0 μm from the substrate. The dry film organic material can bedeposited to build up a layer thickness at a rate of less than about 100nm/sec, to form a first organic layer. A second liquid ink can beapplied to a second transfer surface, the second liquid ink defined by acarrier fluid and dissolved or suspended film-forming organic materialfor forming a layer of an organic light-emitting device. The secondtransfer surface can be energized to substantially evaporate the carrierfluid and form a second dry film organic material on the second transfersurface. The second dry film organic material can be transferred fromthe second transfer surface to the first organic layer such that thesecond dry film organic material is deposited in substantially a solidphase. The dry film organic material can be deposited to build up alayer thickness at a rate of from about 0.1 nm/sec to about 1.0 mm/sec,to form a second organic layer. The index of refraction of the firstorganic layer can be intermediate between an index of refraction of thesemi-transparent or translucent substrate and an index of refraction ofthe second organic layer.

A method of increasing light scattering in an organic light-emittingdevice is provided by the present teachings. The method can comprise anapplying step, an energizing step, a transferring step, and a depositingstep. A liquid ink can be applied to a transfer surface for forming alayer of an organic light-emitting device. The liquid ink can be definedby a carrier fluid and dissolved or suspended film-forming organicmaterial. The transfer surface can be energized to substantiallyevaporate the carrier fluid and form a dry film organic material on thetransfer surface. The dry film organic material can be transferred fromthe transfer surface to a substrate such that the dry film organicmaterial is deposited on the substrate in substantially a solid phase,wherein the transfer surface is positioned at a distance of less thanabout 200 μm from the substrate. The transferred organic film materialcan be deposited to build up a layer thickness at a rate of from about0.1 nm/sec to about 1.0 mm/sec and at a mass deposition rate of fromabout 1.0 ng/sec to about 100 μg/sec, to form a multi-layered roughorganic layer. The multi-layered rough organic layer can comprise fromabout 2 sub-layers to about 200 sub-layers and have a roughness of fromabout 5.0 nm to about 10.0 nm as the root mean squared of surfacethickness deviations in an area 100 μm². In some embodiments, the areameasured is a 10 μm by 10 μm surface. For example, the multi-layeredrough organic layer can comprise from about 2 sub-layers to about 100sub-layers, or from about 2 sub-layers to about 200 sub-layers. Anemitting material can be deposited over the multi-layered rough organiclayer to form an emitting layer and at least part of an organiclight-emitting device stack. An organic light-emitting device stackincluding the multilayered rough organic layer and the emitting layercan exhibit a luminosity efficiency of from about 1.01 to about 2.0,that is, the organic light-emitting device stack can exhibit an increasein luminosity by a factor of from about 1.01 to about 2.0 relative tothe luminosity of the same microcavity but wherein the second surfacehas a surface roughness of less than 5.0 nm expressed as the root meansquare of the surface thickness deviation in an area of 10×10 μm².

An organic light-emitting device stack is provided by the presentteachings. The stack can comprise a substrate. The stack can comprise adry film organic material layer formed on the substrate and comprisingfrom about 2 sub-layers to about 20 sub-layers, a first surface facingthe substrate, and a second surface opposite the first surface. Thestack can comprise an emitting layer over the dry film organic materiallayer such that the dry film organic material layer is between thesubstrate and the emitting layer. The emitting layer can comprise alight-emitting organic material that emits light, upon excitation, at aparticular emission wavelength, for example, a peak wavelength. Thesecond surface can exhibit a surface roughness of from about 0.5 nm toabout 1.0 μm as the root mean squared of surface thickness deviations inan area 10 μm², for example, from about 1.0 nm to about 10.0 nm as theroot mean squared of surface thickness deviations in an area 10 μm². Insome embodiments, the area measured is a 10 μm by 10 μm surface. Theorganic light-emitting device stack can exhibit an increase inluminosity of a factor of from about 1.01 to about 2.0 relative to theluminosity of the same microcavity but with a second surface havingsurface roughness of less than 5.0 nm expressed as the root mean squareof the surface thickness deviation in an area of 10×10 μm². A method offorming a microcavity for an organic light-emitting device is providedby the present teachings. The method can comprise an applying step, anenergizing step, a transferring step, and a depositing step. A liquidink can be applied to a transfer surface for forming a layer of anorganic light-emitting device. The liquid ink can be defined by acarrier fluid and a dissolved or suspended film-forming organicmaterial. The transfer surface can be energized to substantiallyevaporate the carrier fluid and form a dry film organic material on thetransfer surface. The dry film organic material can be transferred fromthe transfer surface to a substrate such that the dry film organicmaterial is deposited on the substrate in substantially a solid phase,to form a first organic buffer layer. The substrate can comprise a firstreflective electrode and the transfer surface can be positioned at adistance of from about 1.0 μm to about 10.0 mm from the substrate duringthe transferring, for example, at a distance of from about 10.0 μm toabout 100.0 μm from the substrate. The dry film organic material can bedeposited to build up a layer thickness at a rate of from about 0.1nm/sec to about 500 nm/sec, for example, at a rate of from about 0.1nm/sec to about 50 nm/sec. A light-emitting organic material can bedeposited over the first organic buffer layer to form an emitting layersuch that the first organic buffer layer is between the substrate andthe emitting layer. A second reflective electrode can be deposited overthe emitting layer such that the emitting layer is between the firstreflective electrode and the second reflective electrode, to form anOLED microcavity. At least one of the first and second reflectiveelectrodes can be semi-transparent or translucent and the firstreflective electrode and the second reflective electrode can beseparated from one another by a distance. The distance can correspond toa depth of the microcavity. The depth of the microcavity can beconfigured for resonance emission of the emission wavelength of thelight-emitting organic material.

A microcavity for an organic light-emitting device is provided by thepresent teachings. The microcavity can comprise a substrate, a dry filmorganic material layer, an emitting layer, and a second reflectiveelectrode. The substrate can comprise a first reflective electrode. Thedry film organic material layer can be formed on the substrate andcomprise a first surface facing the substrate and a second surfaceopposite the first surface. An emitting layer over the dry film organicmaterial layer can be provided such that the dry film organic materiallayer is disposed between the first reflective electrode and theemitting layer. The emitting layer can comprise a light-emitting organicmaterial. The second reflective electrode can be provided over theemitting layer such that the emitting layer is disposed between thefirst reflective electrode and the second reflective electrode. Thesecond surface can exhibit a surface roughness of from about 0.5 nm toabout 1.0 μm as the root mean squared of surface thickness deviations inan area 10×10 μm², for example, a surface roughness of from about 0.5 nmto about 10.0 nm, of from about 1.0 nm to about 1.0 μm, of from about5.0 nm to about 1.0 μm, or of from about 10.0 nm to about 500 nm. Insome embodiments, the area measured is a 10 μm by 10 μm surface. Theorganic light-emitting device stack can exhibit an increase inluminosity of a factor of from about 1.01 to about 2.0 relative to theluminosity of the same microcavity but with a second surface havingsurface roughness of less than 5.0 nm expressed as the root mean squareof the surface thickness deviation in an area of 10×10 μm². The roughsurface interface can be used to separate the microcavity effect whereincolor chromaticity is enhanced from the light outcoupling effect whereinthe luminosity efficiency is enhanced. At least one of the first andsecond reflective electrodes can be semi-transparent or translucent. Thefirst reflective electrode and the second reflective electrode can beseparated from one another by a distance, the distance can correspond toa depth of the microcavity, and the depth of the microcavity can beconfigured for resonance emission of the emission wavelength of thelight-emitting organic material.

BRIEF DESCRIPTION OF THE DRAWINGS

A better understanding of the features and advantages of the presentteaching is provided with reference to the accompanying drawings, whichare intended to illustrate, not limit, the present teachings.

FIG. 1 is a flow chart showing a process flow in accordance with variousembodiments of the present teachings.

FIGS. 2A-2D are schematic drawings of device stacks with layerdeposition sequences in accordance with various embodiments of thepresent teachings.

FIG. 3 is a schematic drawing illustrating a VTE process, a thermalprinting process, or a combination thereof to vary HTM layer thicknessand to tune a device emission spectrum in accordance with variousembodiments of the present teachings.

FIG. 4 is a flow diagram of a method of forming a dried organic layerfor an organic light-emitting device in accordance with variousembodiments of the present teachings.

FIG. 5 is a schematic drawing illustrating three different filmmorphologies formed under various deposition conditions in accordancewith various embodiments the present teachings.

FIG. 6 is a flow diagram of a method of forming a crystalline organiclayer for an organic light-emitting device in accordance with variousembodiments of the present teachings.

FIG. 7 is a schematic diagram illustrating an OLED stack that can beconstructed using a thermal printed low index of refraction holetransport material (HTM) as a light out-coupling layer in accordancewith various embodiments of the present teachings.

FIG. 8 is a flow diagram of a method of decreasing the refractive indexof an organic layer in accordance with various embodiments of thepresent teachings.

FIG. 9 is a flow diagram of a method of increasing light scattering inan organic light-emitting device in accordance with various embodimentsof the present teachings.

FIG. 10A is a schematic representation of the fundamental mode of aFabry-Perot (FP) microcavity where m=1, the corresponding resonantwavelength is equal to λ=2n, and other wavelengths inside the cavity aresuppressed due to the rearranged optical mode density, in accordancewith various embodiments of the present teachings.

FIG. 10B is a schematic representation of the positioning of an EMLrelative to the Fabry-Perot (FP) microcavity shown in FIG. 10A, inaccordance with various embodiments of the present teachings.

FIG. 11 is a schematic representation of a Fabry-Perot (FP) microcavitymode (m=2) that can be achieved in accordance with various embodimentsof the present teachings.

FIG. 12 is a schematic diagram of a device stack and illustrates alight-emitting layer (EML) at an antinode position of a microcavity asused to enhance light emission in accordance with various embodiments ofthe present teachings.

FIG. 13 is a graph showing blue OLED emission chromaticity as a functionof HIL2 thickness (x nm) in accordance with various embodiments of thepresent teachings.

FIG. 14 is a flow diagram of a method of forming a microcavity for anorganic light-emitting device in accordance with various embodiments ofthe present teachings.

DETAILED DESCRIPTION

The present teachings provide an OLED that comprises at least oneorganic layer disposed between, and in electrical connection with, ananode and a cathode. When a current is applied, the anode injects holes,and the cathode injects electrons, into the organic layer. The injectedholes and electrons respectively migrate toward the oppositely chargedelectrode. When an electron and hole localize on the same molecule intothe organic layer, an “exciton” is formed comprising a localizedelectron-hole pair having an excited energy state. Light is emitted whenthe exciton relaxes via a photoemissive mechanism.

According to various embodiments, the present teachings provide a methodfor the application of various layers, including buffer layers, tocontrol the properties of the OLED device or of other organicmulti-layered light-generating structures. For example, a buffer layeror other layer can comprise at least one of a hole injection layer(HIL), a hole transport layer (HTL), an emission layer (EML), anelectron transport layer (ETL), an electron injection layer (EIL), and ablocking layer (BL). Other layers, such as a protective layer, can alsobe incorporated. One or more parameters such as ink concentration,deposition (accumulation) rate, mass deposition rate, bake temperature,and/or bake time, as described herein, can be employed and/or adjustedso that a first baked organic layer, buffer layer, or any other layercan be provided with desired characteristics to make the layer suitablefor one or more OLED applications.

Thermal printing can be controlled by adjusting many parameters. Theparameters can be tuned to change the organic layer structure androughness and thus to create unique features in the organic layer. Bycontrolling thermal printing conditions the structure and properties ofthe organic layer can be controlled such that OLED performance can beenhanced. The film deposition process can involve accumulation of filmmaterial on the substrate whereby the deposited material firstmolecules, then forms clusters, then grow in size to become islands, andthen coalesce to finally form a continuous film. For typical organicmaterials that have low packing densities and strong bondingdirectionality they can be deposited in the amorphous state. Under theinfluence of thermal radiation or in the presence of solvent vapor, theorganic molecules can undergo surface migration, rearrangement orrelaxation during film growth, which as a consequence might lead to thegrowth of columnar structure or crystalline structure, especially athigh deposition rates. Further, if the film undergoes heat treatment andthe viscosity is low enough that the surface tension overcomes theinternal friction, then the film can start to reflow. If the film is notproperly compatible with the underlying substrate, it can start to pullup and dewet from the substrate, as a result it might form some distinctsurface pattern, for example, by spinodal decomposition. The thermalprinting deposited film of the present teachings can, for example, actas a seed layer or a buffer layer to provide a cushion for thedeposition of other layers, for example, the remaining layers, of anOLED stack. Combining thermal printing and post-deposition heattreatment can be used to create distinctive surface patterns in amicroscale or nanoscale. The layer thickness can be changed or surfaceroughness of the organic layer can be changed and such changes can beimplemented to enhance features such as luminosity efficiency.

With reference to the drawings, FIG. 1 is a flow chart showing a processflow 10 in accordance with various embodiments of the present teachings.An OLED substrate 20 can be provided as part of a substrate front end30. HIL/HTL ink 40 can be applied to OLED substrate 20 using thermalprinting 50 in building substrate front end 30. The substrate front end30, after ink transfer, can be subjected to a post-bake treatment 60. Asubstrate back end 70 can then be constructed on the completed front endto form a final OLED 80.

With reference to the remaining drawings, identical reference numbersused in different drawings denote the same layer materials andthicknesses as described in connection with the other drawings. FIGS.2A-2D are schematic drawings of device stacks with layer depositionsequences formed in accordance with the present teachings. The stackseach have a front end (FE), an intervening thermal printing applied holetransport material (HTM) layer 88, and a back end (BE). FIG. 2A is aschematic representation of an OLED stack that can be fabricated inaccordance with the present teachings. The front end of the stack cancomprise an anode 82, an HIL 84, and an HTM layer 86. The back end ofthe stack can comprise an HTL 90, an EML 94, an ETL 96, and a cathode98. Anode 82 can comprise, for example, indium tin oxide (ITO). HIL 84can be 30 nm thick and can comprise, for example, the materialsdescribed in U.S. Patent Application Publication No. US 2011/0057171 A1,which is incorporated herein in its entirety by reference. HTM layer 86can be 20 nm thick and can comprise the material, for example, offormula 2 shown in U.S. Patent Application Publication No. US2007/0134512 A1, which is incorporated herein in its entirety byreference. HTL 90 can be 20 nm thick and can comprise NPB. EML 94 can be30 nm thick. ETL 96 can be 20 nm thick and can comprise the materialsdescribed, for example, in U.S. Patent Application Publication No. US2009/0167162 A1, which is incorporated herein in its entirety byreference. Cathode 98 can comprise lithium fluoride and/or aluminum.

FIG. 2B is a schematic representation of another OLED stack according tothe present teachings. The front end (FE) of the stack can compriseanode 82 and HIL 84. The back end (BE) of the stack can comprise HTL 90,EML 94, ETL 96, and cathode 98.

FIG. 2C is a schematic representation of yet another stack according tovarious embodiments of the present teachings. The front end (FE) of thestack can comprise anode 82 and HIL 84. The back end (BE) of the stackcan comprise HTM layer 86, HTL 90, EML 94, ETL 96, and cathode 98.

FIG. 2D is a schematic representation of yet another stack according tovarious embodiments of the present teachings. The front end (FE) of thestack can comprise anode 82, HIL 84, and HTM layer 86. The back end (BE)of the stack can comprise another HTM layer 86, HTL 90, EML 94, ETL 96,and cathode 98.

The thermal printing method of the present teachings enables filmthickness to be modified by changing any of a number of parameters. Forexample, the method can involve using a specific organic materialconcentration in the liquid ink, print pitch, number of ink drops perpixel, ink drop volume, and/or using specific evaporation conditions(print, temperature, and duration). The ink preparation for depositingan HIL or HTL can take into consideration the specific EML ink that willsubsequently be used. The “front end” (FE) refers to those layersdeposited and steps conducted before thermal printing. The OLED frontend process can include substrate chemical cleaning, rinsing, baking, UVozone treatment, oxygen plasma cleaning, and coating the HIL or HTL byVTE, or other deposition methods. The “backend process” (BE) can includecoating of the HIL or the HTL by VTE, and depositing the EML, the ETL,and an electrode. Depending on whether the process begins with the anodeor the cathode, the layers associated with a FE or BE can be reversed.Examples of some FE and BE processes in accordance with the presentteachings are shown in FIG. 3.

FIG. 3 is a schematic drawing illustrating a VTE process, a thermalprinting process, or a combination thereof, to vary HTM layer thicknessand to tune a device emission spectrum, in accordance with the presentteachings. An OLED stack is shown that comprises anode 82 and HIL 84 onthe front end (FE). The HTM layer 100 is located between the front endand the back end and can be deposited by thermal printing, VTE, or acombination thereof. The back end can comprise HTL 90, EML 94, ETL 96,and cathode 98. Four different embodiments of HTM layer 100 are shown.Embodiment A comprises forming a VTE-HTM layer 102 followed by thermalprinting HTM layer 88. Embodiment B comprises only forming a thermalprinting HTM layer 88. Embodiment C comprises forming a thermal printingHTM layer 88 followed by a VTE-HTM layer 104. Embodiment D comprisesforming a first VTE-HTM layer 102, followed by a thermal printing HTMlayer 88, and then followed by second VTE-HTM layer 104.

FIG. 4 illustrates a method of forming a dried organic layer for anorganic light-emitting device, provided by the present teachings. Themethod can comprise applying, energizing, transferring, and bakingsteps. For example, FIG. 4 is a flow diagram of a method 110 of forminga dried organic layer for an organic light-emitting device in accordancewith the present teachings. An applying step 120 is shown followed by anenergizing step 130, then a transferring step 140, and then a bakingstep 150. A liquid ink can first be applied to a transfer surface forforming a layer of an organic light-emitting device. The liquid ink canbe defined by a carrier fluid and dissolved or suspended film-formingorganic material. The transfer surface can then be energized tosubstantially evaporate the carrier fluid and form a dry film organicmaterial on the transfer surface. The dry film organic material can thenbe transferred from the transfer surface to a substrate such that thedry film organic material is deposited on the substrate in substantiallya solid phase. The transfer surface can be positioned at a distance offrom about 1.0 μm to about 50.0 mm from the substrate during thetransferring, for example, at a distance of from about 10.0 μm to about100.0 μm from the substrate. The dry film organic material can bedeposited to build up a layer thickness at a rate of from about 0.1nm/sec to about 1.0 mm/sec, to form a pre-bake organic layer on thesubstrate. The pre-bake organic layer can be baked at a first baketemperature of from about 50° C. to about 250° C. for a first bake timeof from about 5.0 milliseconds to about 5.0 hours to form a first bakedorganic layer for an organic light-emitting device.

Any type of transfer surface or combination of transfer surface typescan be employed with the methods of the present teachings. Examples oftransfer surface types can include nozzles, flat surfaces, and channels.Any number of transfer surfaces can be employed, and any particulartransfer surface can comprise one or more opening for ejecting orotherwise transferring ink, organic material, or other kinds ofmaterial. The organic material can comprise one or more type of organicmolecule. While “organic material” as described herein includes at leastone kind of organic material, the organic material can also includeimpurities of an inorganic nature, or small amounts of inorganicmaterial.

The transferring step can comprise transferring the organic materialonto a substrate. The transfer surface can be positioned at any desireddistance from substrate during the deposition of the at least oneorganic material, and the distance chosen can be utilized to providedesired characteristics to the deposited organic layer. The distancebetween the transfer surface and the substrate can be, for example, fromabout 1.0 μm to about 500 mm, from about 20 μm to about 10 mm, fromabout 30 μm to about 2.0 mm, from about 10.0 μm to about 100.0 μm, fromabout 40 μm to about 60 μm, or about 50 μm. These distances can also beused in embodiments that do not include a baking step.

The at least one organic material being deposited during the depositingstep can build up a layer thickness at any desired rate to form apre-bake organic layer. For example, the layer thickness can be built upat a rate of from about 0.1 nm/sec to about 1.0 mm/sec, from about 0.5nm/sec to about 750 μm/sec, from about 1.0 nm/sec to about 600 μm/sec,from about 5.0 nm/sec to about 500 μm/sec, from about 10 nm/sec to about400 μm/sec, from about 25 nm/sec to about 250 μm/sec, from about 50nm/sec to about 100 μm/sec, from about 100 nm/sec to about 1.0 μm/sec,from about 150 nm/sec to about 750 nm/sec, or from about 250 nm/sec toabout 500 nm/sec.

The pre-bake organic layer, or any other organic layer deposited can bebaked at any desired temperature for any desired duration. Preferablythe layer is baked at a temperature of at least the glass transitiontemperature of the organic material transferred. The bake temperaturecan be from about 30° C. to about 450° C., from about 40° C. to about400° C., from about 45° C. to about 300° C., from about 50° C. to about250° C., from about 55° C. to about 235° C., from about 60° C. to about220° C., from about 70° C. to about 205° C., from about 80° C. to about180° C., or from about 100° C. to about 160° C.

The bake time duration, or the difference in bake time duration betweentwo different bake times, can be from about 5.0 milliseconds to about5.0 hours, from about 10 milliseconds to about 2.5 hours, from about 50milliseconds to about 1.5 hours, from about 100 milliseconds to about1.0 hour, from about 250 milliseconds to about 30 minutes, from about500 milliseconds to about 15 minutes, from about 1.0 second to about 10minutes, from about 5.0 seconds to about 2.5 minutes, from about 10seconds to about 1.0 minute, from about 15 seconds to about 50 seconds,or from about 20 seconds to about 45 seconds. For example, the bakingcan heat the substrate to an elevated temperature and hold it for aperiod of time, for example, about 3 minutes at from about 150° C. toabout 180° C. The temperature can be close to or above the glasstransition temperature of the HIL or HTL organic material to enable theorganic material to reflow or rearrange, thus minimizing the surfaceroughness. The bake temperature and time can be set so as to not exceeda certain limit such that the layer is prevented from crystallizing orre-evaporating.

The method can be performed any desired number of times to form anydesired number of layers. If multiple baked organic layers are formed,the bake temperature of each subsequent layer should be less than thebake temperature used for baking the previously baked layer or layers.That is, if it is desired to heat to the glass transition temperaturefrom each layer, the glass transition temperature of each subsequentlybaked layer should be less that the glass transition temperature of anyproceeding baked layer so as to prevent or minimize the movement oralteration of the previously baked layers. The difference in baketemperature and/or glass transition temperature of two sequentiallydeposited layers can be from about 1.0° C. to about 500° C., from about15° C. to about 250° C., from about 20° C. to about 100° C., from about25° C. to about 75° C., from about 40° C. to about 70° C., or from about45° C. to about 65° C. For example, the bake temperature for a firstorganic layer can be from about 50° C. to about 250° C., the baketemperature for a second organic layer can be from about 50° C. to about235° C., but less that that used for the first layer, the baketemperature for a third organic layer can be from about 50° C. to about220° C., but less that that used for the second layer, and so on. Insome embodiments, a particular organic layer can be baked at one or moretemperature. The bake time duration for subsequent layers can be thesame as or less that the bake time of the previous layer. For example, asecond bake time can be less than a first bake time, a third bake timecan be less than a second bake time, a fourth bake time can be less thana third bake time, and a fifth bake time can be less than a fourth baketime.

As described in more detail herein, one or more parameters, such as inkconcentration, deposition (transfer/accumulation) rate, mass depositionrate, bake temperature, and/or bake time, can be employed and/or variedto produce organic layers with particular, desired characteristic. Forexample, at least one of the deposition rate and bake time can beadjusted so that the organic layer has a crystalline character.Employing a faster deposition (transfer accumulation) rate, baking at ahigher temperature, and/or baking for a longer bake time can aid inachieving a crystalline layer. At least one of the deposition rate andbake time can be adjusted so that the organic layer has a porouscharacter. In some embodiments, a fast deposition rate, a low baketemperature, and/or a short bake time can help yield a porous layer. Ahigher mass deposition rate, a low bake temperature, and/or a short baketime can be used to produce a rough layer. At least one of thedeposition rate and bake time can be adjusted so that the baked layerhas a rough character.

FIG. 5 is a schematic drawing illustrating three different filmmorphologies formed under various deposition conditions in accordancewith various embodiments of the present teachings. Hole transportmaterial is transferred by thermal printing flux to an anode 82 that cancomprise indium tin oxide layered on a glass substrate. In the stackshown on the left, a thermal printing HTM layer 106 having ananocrystalline morphology is shown formed on anode 82 and covered byVTE-HTM layer 102, HTL 90, EML 94, ETL 96, and cathode 98. In the stackshown in the middle, a thermal printing HTM layer 108 having ananoporous morphology is shown on anode 82, followed by VTE-HTM layer102, HTL 90, EML 94, ETL 96, and cathode 98. In the stack shown on theright, a rough/dense HTM layer 103 is shown on anode 82, followed by anHTL 91, an EML 95, ETL 96, and cathode 98.

The rate of the organic material transferred from the transfer surfacecan be adjusted in terms of the mass of organic material ejected over aparticular period of time. The mass transfer rate can be from about 0.5ng/sec to about 500 μg/sec, from about 1.0 ng/sec to about 100 μg/sec,from about 5.0 ng/sec to about 80 μg/sec, from about 15 ng/sec to about10 μg/sec, from about 50 ng/sec to about 1 μg/sec, from about 100 ng/secto about 500 ng/sec, or from about 200 ng/sec to about 400 ng/sec.

An organic layer can be formed of any desired thickness. The organiclayer can have a thickness of from about 0.5 nm to about 100 μm, fromabout 1.0 nm to about 50 μm, from about 10 nm to about 10 μm, from about20 nm to about 1.0 μm, from about 50 nm to about 500 nm, or from about100 nm to about 300 nm.

An organic layer can be formed of any desired density. The organic layercan have a density of from about 0.1 g/cm3 to about 7.5 g/cm3, fromabout 0.25 g/cm3 to about 5.0 g/cm3, from about 0.5 g/cm3 to about 2.5g/cm3, from about 1.0 g/cm3 to about 2.0 g/cm3, or from about 1.25 g/cm3to about 1.5 g/cm3.

An organic layer can be formed of any desired surface roughness. Theorganic layer can have a surface roughness, expressed as the root meansquare of the surface thickness deviation in an area 10 μm², of fromabout 0.1 nm to about 10 μm, from about 0.25 nm to about 5.0 μm, fromabout 0.5 nm to about 1.0 μm, from about 0.5 nm to about 10.0 nm, fromabout 1.0 nm to about 500 nm, from about 5.0 nm to about 250 nm, fromabout 10 nm to about 125 nm, from about 20 nm to about 100 nm, fromabout 25 nm to about 75 nm, or from about 40 nm to about 50 μm. Forexample, roughness can be provided on a scale of less than 20 nm or lessthan 5 nm. In some embodiments, the area measured is a 10 μm by 10 μmsurface.

The first baked organic layer or any other organic layer describedherein can comprise at least one of a hole injection layer, a holetransport layer, an emission layer, an electron transport layer, anelectron injection layer, and a blocking layer. As used herein, the term“organic” can include small molecule organic materials, as well aspolymers, that can be used to fabricate organic opto-electronic devices.A small molecule can refer to any organic material that is not apolymer, and “small molecules” can be relatively large in size and/ormass. Small molecules can include repeated units. Small molecules canalso be incorporated into polymers, for example, as pendent groups on apolymer backbone or as a part of the backbone. Small molecules can alsoserve as the core moiety of a dendrimer that consists of a series ofchemical shells built on the core moiety. The core moiety of a dendrimercan be a fluorescent or phosphorescent small molecule emitter. Adendrimer can be a “small molecule,” and all dendrimers used in thefield of OLEDs can be small molecules. A small molecule generally has awell-defined chemical formula with a single molecular weight, whereas apolymer has a chemical formula and a molecular weight range or a weightthat can vary from molecule to molecule. As used herein, “organic” alsoincludes metal complexes of hydrocarbon and heteroatom-substitutedhydrocarbon ligands.

Any suitable hole injection material can be employed for a holeinjection layer or other layer. A hole injection layer (HIL) canplanarize or wet the anode surface so as to provide efficient holeinjection from the anode into the hole injecting material. In someembodiments, the hole injection layer can comprise a solution-depositedmaterial, such as a spin-coated polymer, for example, PEDOT:PSS, or itcan comprise a vapor-deposited small molecule material, for example,CuPc or MTDATA. The hole injection layer can also have a charge carryingcomponent having HOMO (Highest Occupied Molecular Orbital) energy levelsthat favorably match up, as defined by their herein-described relativeionization potential (IP) energies, with the adjacent anode layer on afirst side of the HIL, and the hole transporting layer on a second,opposite side of the HIL. The “charge carrying component” is thematerial responsible for the HOMO energy level that actually transportsholes. This component can be the base material of the HIL, or it can bea dopant. Using a doped HIL allows the dopant to be selected for itselectrical properties, and the host to be selected for morphologicalproperties such as wetting, flexibility, toughness, and the like.Properties for the HIL material can be provided such that holes can beefficiently injected from the anode into the HIL material. The thicknessof the HIL can be thick enough to help planarize or wet the surface ofthe anode layer, for example, a thickness of from about 10 nm to about50 nm.

Any suitable hole transport material can be employed for a holetransport layer or other layer. For example, the hole transport layercan include a material capable of transporting holes. The hole transportlayer can be intrinsic (undoped), or doped. Doping can be used toenhance conductivity. α-NPD and TPD are examples of intrinsic holetransport layers. An example of a p-doped hole transport layer ism-MTDATA doped with F₄-TCNQ at a molar ratio of 50:1, as described inUnited States Patent Application Publication No. US 2003/0230980 A1 toForrest et al., which is incorporated herein by reference in itsentirety. Other hole transport layers can be used.

Any suitable light-emitting material can be employed for alight-emitting layer (EML). The EML can comprise an organic materialcapable of emitting light when a current is passed between the anode andcathode. The emitting layer can contain a phosphorescent emissivematerial, although fluorescent emissive materials can instead, oradditionally, be used. Phosphorescent materials can have higherluminescent efficiencies. The emissive layer can also comprise a hostmaterial capable of transporting electrons and/or holes, for example,doped with an emissive material that can trap electrons, holes, and/orexcitons, such that excitons relax from the emissive material via aphotoemissive mechanism. The emitting layer can comprise a singlematerial that combines transport and emissive properties. Whether anemitting material is a dopant or a major constituent, an emitting layercan comprise other materials, such as dopants, that tune the emission ofthe emissive material. An EML can include a plurality of emittingmaterials capable of, in combination, emitting a desired spectrum oflight. Examples of phosphorescent emissive materials include Ir(ppy)₃.Examples of fluorescent emissive materials include DCM and DMQA.Examples of host materials include Alq₃, CBP, and mCP. Examples ofemitting materials and host materials are described in U.S. Pat. No.6,303,238 B1 to Thompson et al., which is incorporated herein byreference in its entirety.

Emitting materials can be included in the EML in a number of ways. Forexample, an emitting small molecule can be incorporated into a polymer.For example, a small molecule can be incorporated into the polymer as aseparate and distinct molecular species, by incorporation into thebackbone of the polymer so as to form a co-polymer, or by bonding as apendant group on the polymer. Other emissive layer materials andstructures can be used. For example, a small molecule emissive materialcan be present as the core of a dendrimer.

Any suitable electron transport material can be employed for theelectron transport layer. The electron transport layer can include amaterial capable of transporting electrons. The electron transport layercan be intrinsic (undoped), or doped. Doping can be used to enhanceconductivity. Alq₃ is an example of an intrinsic electron transportlayer. An example of an n-doped electron transport layer is BPhen dopedwith Li at a molar ratio of 1:1, as described in U.S. Patent ApplicationPublication No. US 2003/02309890 A1 to Forrest et al., which isincorporated herein by reference in its entirety. Other electrontransport layers can instead or additionally be used.

Any suitable electron injection material can be employed for theelectron injection layer. The electron injection layer can be any layerthat improves the injection of electrons into an electron transportlayer. LiF/Al is an example of a material that can be used as anelectron injection layer that injects electrons into an electrontransport layer from an adjacent layer. Other materials or combinationsof materials can be used for injection layers. Examples of injectionlayers are provided in U.S. Patent Application Publication No. US2004/0174116 A1, which is incorporated herein by reference in itsentirety.

Blocking layers can be used to reduce the number of charge carriers(electrons or holes), and/or the number of excitons, that leave the EML.An electron blocking layer can be located between an EML and a HTL toblock electrons from leaving the emissive layer in the direction of theHTL. If included, the hole blocking layer can be located between an EMLand an ETL to block holes from leaving emissive layer in the directionof electron transport layer. Blocking layers can also or instead be usedto block excitons from diffusing out of the emissive layer. The theoryand use of blocking layers is described in more detail in U.S. Pat. No.6,097,147 and United States Patent Application Publication No. US2003/02309890 A1 to Forrest et al., which are herein incorporated byreference in their entireties. A “blocking layer” is a layer that canprovide a barrier that significantly inhibits transport of chargecarriers and/or excitons through the device, without necessarilycompletely blocking the charge carriers and/or excitons. The presence ofsuch a blocking layer in a device can result in substantially higherefficiencies as compared to a similar device that lacks a blockinglayer. A blocking layer can be used to confine emission to a desiredregion of an OLED.

A protective layer can be used to protect underlying layers duringsubsequent fabrication processes. For example, the processes used tofabricate metal or metal oxide electrodes can damage organic layers, anda protective layer can be used to reduce or eliminate such damage. Aprotective layer can have a high carrier mobility for the type ofcarrier that it transports, such that it does not significantly increasethe operating voltage of a device. CuPc, BCP, and various metalphthalocyanines are examples of materials that can be used in protectivelayers. Other materials or combinations of materials can be used. Thethickness of protective layer can be preferably thick enough so thatthere is minimal damage to underlying layers due to fabricationprocesses that occur after an organic protective layer is deposited, yetnot so thick as to significantly increase the operating voltage of adevice. A protective layer can be doped to increase its conductivity.For example, a CuPc or BCP protective layer can be doped with Li.Protective layers can be employed as described in U.S. PatentApplication Publication No. US 2004/0174116 A1, which is incorporatedherein by reference in its entirety.

Materials that can be deposited by the apparatus and methods hereininclude, among other things, organic materials, metal materials, andinorganic semiconductors and insulators, such as inorganic oxides,chalcogenides, Group IV semiconductors, Group III-V compoundsemiconductors, and Group II-VI semiconductors. Any of the followingmaterials or others known in the art can be employed:4,4′-N,N-dicarbazole-biphenyl m-MTDATA4,4′,4″-tris(3-methylphenylphenlyamino)triphenylamine (CBP);8-tris-hydroxyquinoline aluminum (Alq₃);4,7-diphenyl-1,10-phenanthroline (Bphen);tetrafluoro-tetracyano-quinodimethane (F₄-TCNQ);tris(2-phenylpyridine)-iridium (Ir(ppy)₃);2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP); copperphthalocyanine (CuPc); indium tin oxide (ITO);N,N′-diphenyl-N—N′-di(1-naphthyl)-benzidine (NPD);N,N′-diphenyl-N—N′-di(3-toly)-benzidine (TPD);1,3-N,N-dicarbazole-benzene (mCP);4-(dicyanoethylene)-6-(4-dimethylaminostyryl-2-methyl)-4H-pyran (DCM);N,N′-dimethylquinacridone (DMQA); an aqueous dispersion ofpoly(3,4-ethylenedioxythiophene) (PEDOT) with polystyrenesulfonate(PSS); N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine (NPB) and othermaterials described in US 2009/0045739 A1 which is incorporated hereinin its entirety by reference; an electron transport material such asthose described in US 2009/0167162 A1 which is incorporated herein inits entirety by reference; and the hole transport materials described,for example, in US 2007/0134512 A1 which is incorporated herein in itsentirety by reference.

The materials to be transferred or otherwise deposited can be modifiedto make them compatible with a particular deposition method. Forexample, substituents such as alkyl and aryl groups, branched orunbranched, can be used in small molecules to enhance their ability toundergo solution processing. Substituents can be used. Materials withasymmetric structures can have better solution processibility than thosehaving symmetric structures, because asymmetric materials can exhibit alower tendency to recrystallize. Dendrimer substituents can be used toenhance the ability of small molecules to undergo solution processing.

The methods of the present teachings generally employ a thermal printingprinthead to deposit at least one organic layer or other layer on asubstrate. A layer or addition layer can also employ deposition by othermeans such as by vacuum thermal evaporation (VTE). For example, themethod can further comprise depositing at least one organic material orother material on at least one of the substrate and a first bakedorganic layer by vacuum thermal evaporation, to form an organic layer.The vacuum thermal evaporation step can be performed before and/or afterthe thermal printing step. Any combination of thermal printing, vacuumthermal evaporation, or other deposition methods can be employed tobuild up one or more layers. For example, a combination of thermalprinting and vacuum thermal evaporation can be employed to deposit abuffer layer. A combination of thermal printing and vacuum thermalevaporation can be employed to build up at least one of a hole injectionlayer, a hole transport layer, an emission layer, an electron transportlayer, and an electron injection layer.

At least one of the depositing step and the baking step can be performedin an inert atmosphere. Other steps can also be performed in an inertatmosphere. Any suitable inert atmosphere can be employed. For example,an atmosphere comprising nitrogen, helium, neon, argon, krypton, xenon,or any combination thereof can be employed. Non-inert atmospheres canalso be employed. When an inert atmosphere is employed it need not becompletely inert, and can comprise a low level of reactive molecules.

The substrate used in accordance with the present teachings can be anysuitable substrate that provides desired structural properties. Thesubstrate can be flexible or rigid. The substrate can be transparent,semi-transparent, translucent, or opaque. Plastic and glass are examplesof preferred rigid substrate materials. Plastic and metal foils areexamples of preferred flexible substrate materials. The substrate cancomprise a semiconductor material that facilitates the fabrication ofcircuitry. For example, the substrate can comprise a silicon wafer uponwhich circuits are fabricated, and which is capable of controlling OLEDlayers that are subsequently deposited on the substrate. Other substratematerials can be used. The material and thickness of the substrate canbe chosen to obtain desired structural and optical properties.

One or more electrode can be employed in the methods, apparatuses, andsystems of the present teachings. The electrode can comprise an anode ora cathode. The first baked organic layer or another layer can be formedimmediately adjacent the electrode. The first baked organic layer orother layer can be formed directly on the electrode. Methods comprisingthe transfer, deposition, or other application of the first electrodecan further comprise transferring a second electrode on one or morefirst baked organic layers or on a layer deposited thereon, to form anOLED structure. At least one organic layer or other layer can bedeposited between the first baked organic layer and the secondelectrode.

OLEDs are generally (but not always) intended to emit light through atleast one of the electrodes, and one or more transparent electrodes canbe useful in an organic opto-electronic device. For example, atransparent electrode material, such as indium tin oxide (ITO), can beused. A transparent top electrode, such as described in U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated herein by reference intheir entireties, can be used. A transparent bottom electrode can beused instead of, or in combination with, a transparent top electrode.For a device intended to emit light only through one electrode, theother electrode does not need to be transparent, and can insteadcomprise a thick and reflective metal layer having a high electricalconductivity. Similarly, for a device intended to emit light onlythrough one electrode, the other electrode can be opaque and/orreflective. Where an electrode does not need to be transparent, using athicker layer can provide better conductivity, and using a reflectiveelectrode can increase the amount of light emitted through the otherelectrode by reflecting light back toward the transparent electrode.Fully or partially transparent devices can be made in accordance withthe present teachings where both electrodes are at least partiallytransparent. In some embodiments, side-emitting OLEDs can be fabricatedand one or both electrodes can be opaque or reflective in such devices.

The electrode, anode, or cathode, can be constructed out of any suitablematerial or combination of materials. An anode used in accordance withthe present teachings can be any suitable anode that is sufficientlyconductive to transport holes to the organic layers. Anode materials caninclude conductive metal oxides, such as indium tin oxide (ITO) andindium zinc oxide (IZO), aluminum zinc oxide (AlZnO), and metals. Theanode and substrate can be sufficiently transparent to create a devicethat allows emission from the anode side of the OLED stack. An exampleof a transparent substrate and anode combination is a commerciallyavailable ITO (anode) deposited on glass or plastic (substrate).Flexible and transparent substrate-anode combinations are described inU.S. Pat. No. 5,844,363 and U.S. Pat. No. 6,602,540 B2, which areincorporated herein by reference in their entireties. The anode can betranslucent, transparent, semi-transparent, opaque, and/or reflective.The material and thickness of the anode can be chosen to obtain desiredconductive and optical properties. Where the anode is transparent, therecan be a range of thicknesses for a particular material whereby thematerial is thick enough to provide a desired conductivity yet thinenough to provide a desired degree of transparency and, in some cases,flexibility. Other anode materials and structures can be used.

The cathode can comprise any suitable material or combination ofmaterials known in the art such that the cathode is capable ofconducting electrons and injecting them into the organic layers ofdevice. A cathode can be translucent, transparent, semi-transparent,opaque, and/or reflective. Metals and metal oxides are examples ofsuitable cathode materials. The cathode can comprise a single layer, orcan have a compound structure. For example, a cathode can be provided asa compound cathode having a thin metal layer and a thicker conductivemetal oxide layer. In a compound cathode, materials for the thickerlayer can include ITO, IZO, and other materials known in the art. U.S.Pat. Nos. 5,703,436, 5,707,745, U.S. Pat. No. 6,548,956 B2, and U.S.Pat. No. 6,576,134 B2, which are incorporated herein by reference intheir entireties, describe examples of cathodes including compoundcathodes having a thin layer of metal such as Mg:Ag and an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Othercathode materials and structures can be used. Thin film transistors(TFTs) and/or other electronic elements can be incorporated into OLEDs,for example, adjacent the electrodes.

Thermal printing can be carried out using the methods and inks asdescribed in U.S. Patent Application Publications Nos. US 2008/0311307A1, US 2008/0308037 A1, US 2006/0115585 A1, US 2010/0188457 A1, US2011/0008541 A1, US 2010/0171780 A1, and US 2010/0201749 A1, which areincorporated herein by reference in their entireties. An ink dispenserand a transfer surface, for example, a nozzle, which, in combination,can together comprise a printhead, can be employed. The ink dispensercan comprise, for example, an inkjet, and the transfer surface can beadapted to discharge a film of material in a substantially dry or solidform. An inkjet dispenser having any number of openings (orifices) forejecting liquid ink onto/into one or more transfer surfaces can beemployed. Upon activation, ink droplets can be ejected from a chamber.The activation means (for example, energy source or sources, such asthermal and/or mechanical) for ejecting ink can be configured so thatmultiple droplets are ejected substantially simultaneously. In addition,or instead, the activation means can be configured so that the pluraldroplets are ejected serially from each orifice. Droplets can bedeposited onto a single target micro-pore array utilizing orificesdirected at the array from plural ink-holding chambers. Each of multiplechambers associated with a target micro-pore array can include one ormore orifices for delivering liquid ink droplets thereto.

Discharge devices that can be employed include those described, forexample, in U.S. Patent Application Publication No. US 2006/0115585 A1,which is incorporated herein by reference in its entirety. An exemplaryapparatus for deposing an organic material on a substrate can include ahousing having a transfer surface, for example, a nozzle, at one end anda reservoir (chamber) at another end. The reservoir can contain organicconstituents used for forming an OLED film. The organic constituent canbe liquid, solid, or a combination thereof. A heat source can beprovided to heat the reservoir and the contents thereof. The heat sourcecan provide heating, for example, to temperatures of from about 100° C.to about 700° C. The heat source or other heater can be activated in apulse-like manner to provide heat to a discharge device cyclically. Theapparatus housing can optionally include an inlet and an outlet. Theinlet and outlet can be defined by a flange adapted to receive a carriergas (interchangeably, transport gas.) The carrier gas can be anysuitable gas or combination of gasses, for example, an inert gas such asnitrogen, argon, or other inert gas described herein. A delivery pathcan be formed within the housing to guide the flow of the carrier gas.Thermal shields can be positioned to deflect thermal radiation from theheat source so as to protect the discharge device and organic particlescontained therein or thereon. Carrier gasses need not be employed andare not used according to various embodiments. Proximity and favorableconcentration gradients between a transfer surface and a substrate canaid in transfer of organic or other material.

An exemplary apparatus for depositing a material on a substrate cancomprise a chamber, plural orifices, a transfer surface, and one or moremicro-porous conduits referred to as micro-pores. The chamber canreceive ink in liquid form and communicate the ink from the orifices tothe transfer surface. The ink can comprise, for example, suspended ordissolved particles in a carrier liquid or solvent. These particles cancomprise, for example, single molecules or atoms, aggregations ofmolecules and/or atoms, or any combination thereof. The transfer surfacecan comprise micro-pores separated by partitions. Micro-pores caninclude micro-porous material therein. A surface of transfer surfaceproximal to the orifices can define inlet ports to the transfer surfacewhile the distal surface of transfer surface, which faces away from theorifices, can define outlet ports. A substrate can be positionedproximal to the outlet ports of the transfer surface, for receiving inkdeposited therefrom. The pores can be of any suitable size. For example,the pore size can be from about 5.0 nm to about 100 μm.

A heater can be added to the chamber for heating and/or dispensing inkor other organic material. Any suitable heater can be used, for example,a MEMS heater. The heater can comprise any thermal energy source(s)operably coupled to the chamber and/or orifices for providing pulsatingenergy to the liquid ink and thereby discharging a respective droplet ofthe liquid ink through each orifice. The heater can deliver heat inpulses having a duration of one minute or less. The heater can beenergized with square pulses having a variable duty cycle and a cyclefrequency of 1 kHz. The heater energy can be used to meter the quantityof ink or other organic material delivered from the chamber to thedischarge nozzle. The chamber can also contain material, other than ink,useful for forming a film or other layer used in the fabrication of anOLED or transistor. Orifices can be configured such that surface tensionof the liquid in the chamber prevents discharge of the liquid prior toactivation of the mechanism for dispensing the ink. Any suitable energysource can be coupled to the chamber, which is capable of providingenergy sufficient to eject droplets of liquid ink from the orifices.Exemplary sources include, for instance, mechanical and vibrationalsources. A piezoelectric material can be used instead of, or in additionto, the heater. Each orifice can be coupled to a separate heater and/orpiezoelectric material. For example, three heating elements can beprovided, one for, and proximate to, each orifice.

A transfer surface or other discharge device can include partitions (orrigid portions) separated by conduits or micro-pores. The micro-poresand rigid portions can collectively define a micro-porous environment.The micro-porous environment can comprise a variety of materials,including, for example, micro-porous alumina or solid membranes ofsilicon or silicon carbide, and which have micro-fabricated pores.Micro-pores are configured to prevent the material dissolved orsuspended in the liquid from escaping through the transfer surface untilthe medium is appropriately activated. When the discharged droplets ofliquid encounter the transfer surface, the liquid is drawn into themicro-pores with assistance from capillary action. The liquid in the inkcan evaporate prior to activation of the discharge nozzle, leavingbehind a coating of the suspended or dissolved particles on themicro-pore walls.

The carrier liquid can comprise, for example, one or more solvents. Theliquid in the ink can comprise one or more solvents having arelatively-low vapor pressure. Alternatively, or in addition, the liquidin the ink can comprise one or move solvents with a relatively-highvapor pressure. The one or more solvents can have a vapor pressure suchthat during the transportation and deposition process the solvent issubstantially evaporated and the plurality of particles that werecarried by the carrier liquid are deposited as solid particles. Thus,the deposited plurality of solid particles can comprise a film or layeron the substrate. The concentration of the particles in the carrierliquid can be measured using any suitable metric. For example, solidscontent in the liquid ink can be used as a concentration measure.

The evaporation of the liquid in the ink can be facilitated oraccelerated by heating the transfer surface. The evaporated liquid canbe removed from the chamber and subsequently collected, for instance, byflowing gas over one or more face of the transfer surface. Depending onthe desired application, micro-pores can provide conduits (or passages)having a minimum linear cross-sectional distance W of a few nanometersto hundreds of microns. The micro-porous region comprising the transfersurface or other discharge device can take a different shape and cover adifferent area (for example, rectangular, L-shaped, triangular,chevron-shaped, and the like) depending on the desired application, witha typical maximum linear cross-sectional dimension DL ranging from a fewhundred nanometers to tens or hundreds of millimeters. In oneembodiment, the ratio of W/D is in a range of from about 1/5 to about1/1000.

The transfer surface can be actuated by a heater, for example, by anozzle heater. A heater can be positioned proximal to the transfersurface. Any type of heater can be used, for example, a MEMS heater. Theheater can comprise a thin metal film. The thin metal film can comprise,for example, platinum. When activated, the heater can provide pulsatingthermal energy to the transfer surface, which acts to dislodge thematerial contained within the micro-pores or conduits. The material cansubsequently be transferred from the transfer surface. In someembodiments, the pulsations can be variable on a time scale of oneminute or less. The transfer surface can be adapted to heat the materialon the transfer surface to a desired temperature or temperatures, oracross a range of temperatures. For example, the heater can heat thematerial on a transfer surface to one or more temperatures within arange of from about 75° C. to about 500° C., or from about 100° C. toabout 400° C.

Dislodging the ink particles can occur, for example, throughvaporization, either by sublimation or by melting and subsequentboiling. The material (for example, ink particles in a carrier liquid)on a transfer surface can be initially heated, for example, to about100° C., to evaporate carrier liquids. The remaining solids (forexample, ink particles which are free, or substantially free, ofsolvents) are then heated, for example, to about 300° C., such that theyare turned into a gas. Thereafter, the gas can be deposited onto asubstrate, where it solidifies. One or more films can be formed thereby.Particles can include, for example, anything from a single molecule oratom to a cluster of molecules or atoms, or a combination thereof. Anysuitable energy source coupled to the transfer surface or otherdischarge device can be employed that is capable of energizing thetransfer surface or other discharge device to thereby discharge thematerial from the micro-pores. In an example, mechanical (for example,vibrational) energy is used. In one embodiment of the present teachings,a piezoelectric material can be used instead of, or in addition to, oneor more heaters.

A solvent-free material can be deposited on a substrate, for example,with a print-head having a multi-orifice inkjet, in accordance with thepresent teachings. Further, multiple print-heads can be arrayed in anapparatus having multiple transfer surfaces, each with a correspondingmulti-orifice inkjet. Still further, one or more reservoirs can supplyliquid ink to the chamber(s) of a print-head apparatus. Print-heads canbe arrayed together with multiple reservoirs supplying ink to one ormore associated liquid-holding chambers. A target array of micro-poresintended to receive liquid ink can be circumscribed by a retaining wallwhich forms a confining well to mechanically confine ink, and/or othermaterial, supplied to the inlets of the micro-pores. The positioningsystem can be employed for adjusting the position of the print-head orprint-head array. A substrate-positioning system can be employed. Thesidewalls of the micro-pores can have defined non-cylindricalgeometries, for example, they can be tapered such that the diameter ofeach micro-pore increases in a direction from the inlet end to theoutlet end. A control system can be provided for controlling aprint-head having a multi-orifice liquid-holding chamber and a transfersurface.

The present teachings are not limited to the deposition of organiclayers and can also, or in the alternative, include deposition of metalmaterial onto a substrate. The deposited metal material can be depositedin substantially solid form. The deposited material can include metalformed utilizing organo-metallic precursor materials dissolved orsuspended in a solvent, or metal dissolved or suspended in a solvent.The metal dissolved or suspended in a solvent can comprise, at leastpartially, nanoparticles, which can be coated with organic compounds.The metal can comprise, for instance, gold, silver, aluminum, magnesium,or copper. The metal can comprise an alloy or mixture of multiplemetals. Such metal material is useful in many applications, forinstance, as a thin film electrode, as an electrical interconnectionbetween electronic circuit elements, and for forming passive absorptiveor reflective patterns. Metal films deposited by the discharge apparatuscan be used to deposit the electrodes and electrical interconnectionsutilized in circuits including organic electronic devices such as OLEDs,transistors, photodetectors, solar cells, and chemical sensors.Organo-metallic or metallic material can be delivered to the transfersurface or other discharge device, and upon activation of the transfersurface, can be delivered to the substrate. A reaction converting theorgano-metallic material into metallic material can be carried out priorto, and/or can occur during, delivery of the liquid from the chamber tothe transfer surface, delivery from the discharge nozzle to thesubstrate, or following deposition on the substrate.

Inorganic semiconductor or insulator material in substantially solidform can be deposited onto a substrate in accordance with the presentteachings. The deposition material can include organic and inorganicprecursor materials dissolved or suspended in a carrier liquid, orinorganic semiconductor or insulator material dissolved or suspended ina carrier liquid. The inorganic semiconductor or insulator materialdissolved or suspended in a liquid can comprise (all, or in part)nanoparticles, which can be coated with organic compounds. The inorganicsemiconductor or insulator can comprise, for instance, group IVsemiconductors (for instance, carbon, silicon, germanium), group III-Vcompound semiconductors (for instance, gallium nitride, indiumphosphide, gallium arsenide), group II-VI compound semiconductors (forinstance, cadmium selenide, zinc selenide, cadmium sulfide, mercurytelluride), inorganic oxides (for instance, indium tin oxide, aluminumoxide, titanium oxide, silicon oxide), and chalcogenides. The inorganicsemiconductor or insulator can comprise an alloy or mixture of multipleinorganic compounds. The semiconductor or insulator material can beuseful in many applications, for instance, as a transparent conductorfor an electrode, as an electrical interconnection between electroniccircuit elements, as an insulating and passivation layer, and as anactive layer in an electronic or optoelectronic device. When integratedtogether, these layers can be utilized in circuits containing organicelectronic devices such as OLEDs, transistors, photodetectors, solarcells, and chemical sensors.

The present teachings can employ the thermal printing apparatuses,systems, and methods as described in U.S. Patent Application PublicationNo. US 2010/0201749 A1, which is incorporated herein by reference in itsentirety. The thermal printing operation can include OLED printing andthe printing material can include a suitable ink composition. In anexemplary embodiment, the printing process can be conducted at aload-locked printer housing having one or more chambers. Each chambercan be partitioned from the other chambers by physical gates or fluidiccurtains. The controller can coordinate transportation of a substratethrough the system and purges the system by timely opening appropriategates. The substrate can be transported using gas bearings which areformed using a plurality of vacuum and gas input portals. The controllercan also provide a non-oxidizing environment within the chamber using agas similar to, or different from, the gas used for the gas bearings.The controller can also control the printing operation by energizing theprint-head at a time when the substrate is positioned substantiallythereunder. The controller can identify the location of the substratethrough the load-locked print system and dispense ink from theprint-head only when the substrate is at a precise location relative tothe printhead. Printing registration can be employed, which refers tothe alignment and the size of one printing process with respect to theprevious printing processes performed on the same substrate. Printingregistration can comprise pattern recognition. Substrate misalignmentsuch as translational misalignment, rotational misalignment,magnification misalignment and combinational misalignment, can becorrected.

The present teachings can employ the thermal printing apparatuses,systems, and methods as described in U.S. patent application Ser. No.12/954,910, filed Nov. 29, 2010, which is incorporated herein byreference in its entirety. In particular, the transfer members, materialcompositions, solutions, and suspensions of the application areincorporated by reference. An OLED film or layer can be formed byproviding a quantity of liquid ink to a transfer surface. The liquid inkcan be defined by a carrier fluid containing dissolved or suspended filmmaterial. The liquid ink can be organized into a prescribed pattern onthe transfer surface with the assistance of a micro-patterned structure.The transfer surface can be energized to substantially evaporate thecarrier fluid to form dry film material on the transfer surface. Thefilm material can be transferred from the transfer surface to thesubstrate such that the film material deposits in substantially thesolid phase. The film material deposited onto the substrate can have apatterned shape or can be a uniform coating over the entire depositionarea.

An example of a liquid ink is film material dissolved or suspended in acarrier fluid. Another example of a liquid ink is pure film material inthe liquid phase, such as film material that is liquid at the ambientsystem temperature or film material that is maintained at an elevatedtemperature so that the film material forms a liquid melt. An example ofa solid ink is one that comprises solid particles of film material.Another example of a solid ink is a film material dispersed in a carriersolid. An example of a gas vapor ink is vaporized film material. Anotherexample of a gaseous vapor ink is vaporized film material dispersed in acarrier gas. The ink can deposit on the transfer surface as a liquid ora solid, and such phase can be the same as or different than the phaseof the ink during delivery. In an example, the film material can bedelivered as gaseous vapor ink and deposited on the transfer surface inthe solid phase. In another example, the film material can be deliveredas a liquid ink and deposited on the transfer surface in the liquidphase. The ink can deposit on the transfer surface in such a way thatonly the film material deposits and the carrier material does notdeposit; the ink can also deposit in such a way that the film materialas well as one or more of the carrier materials deposits.

One or more parameters such as ink concentration, deposition(transfer/accumulation) rate, mass deposition rate, bake temperature,and/or bake time, as described herein, can be employed and/or adjustedso that a first baked organic layer or other layer is provided with acrystalline character. Any desired scale, type, or degree ofcrystallinity can be achieved. For example, microcrystallinity ornanocrystallinity can be achieved. A layer can comprise one or more of acrystalline region and an amorphous region. The organic layer formed canhave a percent of crystallinity of less than 1.0%, from about 1.0% toabout 100%, from about 5.0% to 90%, from about 20% to about 70%, fromabout 30% to about 60%, or from about 40% to about 60%, by either weightpercent or volume percent of the weight or volume of a given layer or achosen portion thereof. Crystallinity of a layer can be measured orexpressed by any suitable means. For example, crystallinity can bemeasured by grain size. In some embodiments, crystallinity is measuredby average grain size.

The crystallinity of an organic layer or other layer can have a grainsize, for example, an average grain size, of less than about 0.5 nm,from about 0.5 nm to about 500 μm, from about 10 nm to about 250 μm,from about 50 nm to about 100 μm, from about 100 nm to about 10 μm, fromabout 500 nm to about 5.0 μm, or from about 200 nm to about 1.0 μm. Amethod of forming a crystalline organic layer for an organiclight-emitting device is provided by the present teachings. The methodcan comprise an applying step, an energizing step, a transferring step,and a baking step. For example, FIG. 6 is a flow diagram of a method 210of forming a crystalline organic layer for an organic light-emittingdevice in accordance with the present teachings. An applying step 220 isshown followed by an energizing step 230, a transferring step 240, and abaking step 250. A liquid ink can be applied to a transfer surface forforming a layer of an organic light-emitting device. The liquid ink canbe defined by a carrier fluid and dissolved or suspended film-formingorganic material. The transfer surface can be energized to substantiallyevaporate the carrier fluid and form a dry film organic material on thetransfer surface. The dry film organic material can have a glasstransition range. The dry film organic material can be transferred fromthe transfer surface to a substrate such that the dry film organicmaterial is deposited on the substrate in substantially a solid phase.The transfer surface can be positioned at a distance of from about 1.0μm to about 10.0 mm from the substrate during the transferring, forexample, at a distance of from about 10.0 μm to about 100.0 μm from thesubstrate. The dry film organic material can be deposited to build up alayer thickness at a rate of from about 0.1 nm/sec to about 1.0 mm/sec,to form a pre-bake organic layer on the substrate. The pre-bake organiclayer can be baked at a bake temperature of from within the glasstransition range to above the glass transition range to form acrystalline organic layer for an organic light-emitting device. Thecrystalline organic layer can have a conductivity of from about 1.0×10⁻⁹S/m to about 1.0×10⁻⁷ S/m.

Imparting crystallinity to one or more layers is advantageous ascrystallinity can increase the conductivity of the layer. Crystallinityis particularly advantageous for a layer adjacent an electrode of anOLED stack. Crystallinity can be imparted to one or more of a holeinjection layer, a hole transport layer, an emission layer, an electrontransport layer, an electron injection layer, or a blocking layer. Acrystalline layer or any other layer can be provided with any suitableconductivity. For example, the conductivity can be less than about1.0×10⁻⁹ S/m, from about 1.0×10⁻⁹ S/m to about 1.0×10⁻⁷ S/m, from about2.5×10⁻⁹ S/m to about 7.5×10⁻⁸ S/m, from about 5.0×10⁻⁹ S/m to about5.0×10⁻⁸ S/m, from about 7.5×10⁻⁹ S/m to about 1.0×10⁻⁸ S/m, or ofgreater than about 1.0×10⁻⁷ S/m. The conductivity can be changed byorders of magnitude by changing the properties of the layer. Forexample, adding impurities into an organic layer can be used to changethe conductivity of the layer from 10⁻⁹ S/m to 10⁻¹ S/m.

One or more parameters such as ink concentration, deposition(transfer/accumulation) rate, mass deposition rate, bake temperature,and/or bake time, as described herein, can be employed and/or adjustedso that a first baked organic layer or other layer is provided with aporous character. A porous character is advantageous for a layer as itcan reduce the index of refraction of the layer and bring the indexcloser to the index of refraction of a substrate, such as a glasssubstrate, for an OLED display. Any suitable index of refraction can beprovided for a porous organic layer. The organic porous layer can havean index of refraction of less than about 1.01, from about 1.01 to about1.60, from about 1.10 to about 1.50, from about 1.20 to about 1.40, fromabout 1.25 to about 1.35, or of greater than about 1.60. The index ofrefraction of the first organic layer or other layer can be intermediatebetween a refractive index of a semi-transparent or translucentsubstrate and a refractive index of a second organic layer. For example,the index of refraction of the semi-transparent or translucent substratecan be from about 1.01 to about 1.55 and the index of refraction of thesecond organic layer can be from about 1.60 to about 5.01. In someembodiments, the index of refraction of the second organic layer is fromabout 1.60 to about 1.80.

An organic light-emitting device is also provided in accordance with thepresent teachings. The device can comprise a first electrode, acrystalline organic layer, an emitting layer, and a second electrode.The crystalline organic layer can be provided over and electricallyassociated with the first electrode and can exhibit a conductivity offrom about 1.0×10⁻⁹ S/m to about 1.0×10⁻⁷ S/m. The emitting layer can beprovided over and electrically associated with the crystalline organiclayer. The emitting layer can comprise a light-emitting organic materialthat emits light, upon excitation, at an emission wavelength. The secondelectrode can be provided over and electrically associated with theemitting layer. Organic material, upon excitation, emits light across arange of wavelengths. The range of wavelengths can fluctuate based onenvironmental conditions such as humidity and temperature. Generally,the wavelength range is relatively narrow, for example, 5.0 nm to about10 nm at one half of the height of the intensity of the peak emissionwavelength within the range. For purposes of the present disclosure, thenominal fluctuations in the emission wavelength range can be ignored forcalculation of microcavity dimensions. The microcavity and structures ofthe present teachings are configured to resonate the peak emissionwavelength of the organic light emitting material exhibited under normaloperating conditions.

FIG. 7 is a schematic diagram illustrating an OLED stack that can beconstructed using a thermal printed low index of refraction holetransport material (HTM) layer as a light out-coupling layer inaccordance with the present teachings. The low index of refraction HTMlayer is used to inject and/or transport charge and to out-couple light.The nanoporous layer (np-HTM) has an index of refraction that is lessthan the “α-HTM” layer, which can be expressed as n(α-HTM)>n(np-HTM).The stack comprises anode 82, nanoporous HTM layer 109, an α-HTM layer105, HTL 91, EML 95, EIL 96, and cathode 98.

A method of decreasing the refractive index of an organic layer isprovided in accordance with the present teachings. The method cancomprise an applying step, an energizing step, and a transferring step,which together can be repeated for multiple applications of variousliquid inks. For example, FIG. 8 is a flow diagram of a method 310 ofdecreasing the refractive index of an organic layer in accordance withthe present teachings. An applying step 320 is shown followed by anenergizing step 330, and a transferring step 340. A second applying step350 is also shown, followed by a second energizing step 360, and asecond transferring step 370. A liquid ink can be applied to a transfersurface for forming a layer of an organic light-emitting device. Theliquid ink can be defined by a carrier fluid and dissolved or suspendedfilm-forming organic material. The transfer surface can be energized tosubstantially evaporate the carrier fluid and form a dry film organicmaterial on the transfer surface. The dry film organic material can betransferred from the transfer surface to a semi-transparent ortranslucent electrode disposed on a semi-transparent or translucentsubstrate such that the dry film organic material is deposited on thesemi-transparent or translucent electrode in substantially a solidphase. The transfer surface can be positioned at a distance of fromabout 1.0 μm to about 10.0 mm from the substrate during thetransferring, for example, at a distance of from about 10.0 μm to about100.0 μm from the substrate. The dry film organic material can bedeposited to build up a layer thickness at a rate of less than about 100nm/sec, to form a first organic layer. A second liquid ink can then beapplied to a second transfer surface or to the same first transfersurface. The second liquid ink can be defined by a carrier fluid anddissolved or suspended film-forming organic material for forming a layerof an organic light-emitting device. The second transfer surface can beenergized to substantially evaporate the carrier fluid and form a seconddry film organic material on the second transfer surface. The second dryfilm organic material can be transferred from the second transfersurface to the first organic layer such that the second dry film organicmaterial is deposited in substantially a solid phase. The dry filmorganic material can be deposited to build up a layer thickness at arate of from about 0.1 nm/sec to about 1.0 mm/sec, to form a secondorganic layer. The index of refraction of the first organic layer can beintermediate between the index of refraction of the semi-transparent ortranslucent substrate and the index of refraction of the second organiclayer.

In accordance with the present teachings, a porous buffer layer can befirst deposited on top of an ITO (anode) by printing far from thesubstrate surface, for example, from a distance of greater than about200 μm. The great distance allows super saturated organic vapor tocondense and molecules to aggregate in free space before arriving ontothe substrate. Then, a deposition step follows at a closer gap, forexample, at a distance of less than about 100 μm, so that the film canbe dense. The bottom porous layer can exhibit a lower index ofrefraction (% related to the porosity) while the top dense layer isrough enough to enhance charge transport and injection into the EML. Theoverall device efficiency can increase. An exemplary stack using such aconstruction is shown in FIG. 7. Porosity can be, for example,nanoporous and/or microporous.

One or more parameters such as ink concentration, deposition(transfer/accumulation) rate, mass deposition rate, bake temperature,and/or bake time, as described herein, can be employed and/or adjustedso that a first baked organic layer or other layer is provided with arough character. Imparting a rough character to one or more layer of anOLED is advantageous as it can promote light scattering and result inincreased luminosity efficiency in view of the current or voltageapplied and the amount of light leaving the OLED. A layer can beprovided with any desirable roughness, for example, so as to achieve aparticular luminosity efficiency when the layer is incorporated into anOLED stack or display. Such an OLED can exhibits a an increase inluminosity by a factor of from about 1.01 to about 2.0, from about 1.10to about 1.90, from about 1.20 to about 1.80, from about 1.30 to about1.70, from about 1.40 to about 1.60, or of greater than about 2.0,relative to the luminosity of a microcavity with the same surface buthaving a surface roughness of less than 5.0 nm expressed as the rootmean square of the surface thickness deviation in an area of 10×10 μm².Incorporation of a rough organic layer into an OLED using one or moremethod of the present teachings can increase luminosity by a desiredfactor.

A method of increasing light scattering in an organic light-emittingdevice is provided by the present teachings. The method can comprise anapplying step, an energizing step, a transferring step, and a depositingstep. For example, FIG. 9 is a flow diagram of a method 410 ofincreasing light scattering in an organic light-emitting device inaccordance with the present teachings. An applying step 420 is shownfollowed by an energizing step 430, a transferring step 440, and adepositing step 450. A liquid ink can be applied to a transfer surfacefor forming a layer of an organic light-emitting device. The liquid inkcan be defined by a carrier fluid and dissolved or suspendedfilm-forming organic material. The transfer surface can be energized tosubstantially evaporate the carrier fluid and form a dry film organicmaterial on the transfer surface. The dry film organic material can betransferred from the transfer surface to a substrate such that the dryfilm organic material is deposited on the substrate in substantially asolid phase, wherein the transfer surface is positioned at a distance ofless than about 200 μm from the substrate. The transferred organic filmmaterial can be deposited to build up a layer thickness at a rate offrom about 0.1 nm/sec to about 1.0 mm/sec. The transferred organic filmmaterial can be deposited and at a mass deposition rate of from about1.0 ng/sec to about 100 μg/sec, to form a multi-layered rough organiclayer. The multi-layered rough organic layer can comprise from about 2sub-layers to about 20 sub-layers and can have a roughness of from about5.0 nm to about 1.0 μm as the root mean squared of surface thicknessdeviations in an area of 10 μm². In some embodiments, the area measuredis a 10 μm by 10 μm surface. An emitting material can be deposited overthe multi-layered rough organic layer to form an emitting layer and toform an organic light-emitting device stack. The organic light-emittingdevice stack can exhibit an increase in luminosity by a factor of fromabout 1.01 to about 2.0 relative to the luminosity of a microcavityhaving the same surface but with a surface roughness of less than 5.0 nmexpressed as the root mean square of the surface thickness deviation inan area of 10×10 μm².

An organic light-emitting device stack is provided by the presentteachings. The stack can comprise a substrate. The stack can comprise adry film organic material layer formed on the substrate and comprisingfrom about 2 sub-layers to about 300 sub-layers, a first surface facingthe substrate, and a second surface opposite the first surface. Forexample, the multi-layered rough organic layer can comprise from about 2sub-layers to about 100 sub-layers, or from about 2 sub-layers to about20 sub-layers. When each sub-layer comprises a mono-molecular layer, themulti-layered rough organic layer can comprise from about 2 sub-layersto about 300 sub-layers, from about 10 sub-layers to about 200sub-layers, or from about 50 sub-layers to about 150 sub-layers. Themulti-layered rough organic layer can have a thickness, for example, offrom about 2 nm to about 300 nm, from about 20 nm to about 200 nm, orfrom about 50 nm to about 150 nm. The stack can comprise an emittinglayer over the dry film organic material layer such that the dry filmorganic material layer is between the substrate and the emitting layer.The emitting layer can comprise a light-emitting organic material thatemits light at an emission wavelength. The second surface can exhibit asurface roughness of from about 0.5 nm to about 1.0 μm as the root meansquared of surface thickness deviations in an area of 10 μm², forexample, from about 1.0 nm to about 500 nm, from about 5.0 nm to about500 nm, or from about 0.5 nm to about 10 nm. In some embodiments, thearea measured is a 10 μm by 10 μm surface. The organic light-emittingdevice stack can exhibit an increase in luminosity by a factor of fromabout 1.01 to about 2.0 relative to the luminosity of the samemicrocavity but with a surface having a surface roughness of less than5.0 nm expressed as the root mean square of the surface thicknessdeviation in an area of 10×10 μm².

The present teachings can employ one or more of the apparatuses,systems, methods, inks, organic materials, inorganic materials, films,layers, electrodes, and/or thin film transistors (TFTs) described in:U.S. Pat. No. 5,405,710, U.S. Pat. No. 6,811,896 B2, U.S. Pat. No.6,861,800 B2, U.S. Pat. No. 6,917,159 B2, U.S. Pat. No. 7,023,013 B2,and U.S. Pat. No. 7,247,394 B2; U.S. Patent Application PublicationsNos. US 2006/0115585 A1, US 2007/0286944 A1, US 2008/0238310 A1, US2008/0311289 A1, US 2008/0311307 A1, US 2009/0115706 A1, US 2009/0220680A1, US 2010/0171780 A1, US 2010/0188457 A1, US 2010/0201749 A1 and US2011/0008541 A1; U.S. patent application Ser. No. 12/954,910, filed Nov.29, 2010; Geffroy et al., “Organic light-emitting diode (OLED)technology: material devices and display technologies,” Polym., Int.,55:572-582 (2006); Chin, “Effective hole transport layer structure fortop-emitting organic light emitting devices based on laser transferpatterning,” J. Phys. D: Appl. Phys. 40:5541-5546 (2007); Huang et al.,“Reducing Blueshift of Viewing Angle for Top-emitting OrganicLight-Emitting Devices” (2008); Lee et al., “Microcavity Effect ofTop-Emission Organic Light-Emitting Diodes Using Aluminum Cathode andAnode,” Bull. Korean Chem. Soc., 2005, Vol. 26, No. 9; OrganicElectronics: Materials, Processing, Devices, and Applications, (So,ed.), CRC Press New York (2010); Bulovic et al., Phys., Rev. B 58: 3730(1998); and Lee et al., Appl. Phys. Lett. 92 (2008) 033303, which areincorporated herein by reference in their entireties.

The use of a microcavity in an OLED device has been shown to reduce theemission bandwidth and improve the color purity, or chromaticity, ofemission, see, for example, U.S. Pat. No. 6,326,224 B1, which isincorporated herein by reference herein in its entirety. A microcavitycan also significantly change the angular distribution of the emissionfrom an OLED device. One or more methods of the present teachings can beemployed to form one or more OLED microcavities. One or more parameterssuch as ink concentration deposition (accumulation) rate, massdeposition rate, bake temperature, and/or bake time, as describedherein, can be employed and/or adjusted to form an OLED microcavity. Thelength and depth of a microcavity can be adjusted by the application ofan organic buffer layer. The organic buffer layer can comprise any ofthe thermal printing formed layers described herein. The OLEDmicrocavity comprises a light-emitting layer and first and secondreflective electrodes. The emitting layer can be spaced from the firstreflective electrode by a first distance and spaced from the secondreflective electrode by a second distance. The first and seconddistances can be optimized for maximal luminosity of the microcavityduring operation. In constructing an OLED microcavity, a depositing stepcan comprise depositing a first organic buffer layer, or other layer,directly onto the first reflective electrode. The first organic emittinglayer can comprise or be deposited directly onto a buffer layer. Thefirst organic buffer layer or other layer can comprise at least one of ahole injection layer, a hole transport layer, an emission layer, anelectron transport layer, and an electron injection layer.

FIGS. 10A and 10B are schematic representations of the fundamental modeof a Fabry-Perot (FP) microcavity where m=1, and the correspondingresonant wavelength is equal to λ=2n. Other wavelengths due to therearranged optical mode density inside the cavity are suppressed. Asimple co-planar FP microcavity can have a pair of mirrors ofreflectance R and spacing d shown by the arrow in FIG. 10A. The resonantcondition of this cavity should satisfy the equation (for optical mode).When the cavity spacing d is doubled (m=2 or =λ/n), there is one modeoverlapped with the emission curve (standing wave) between the tworeflectors. For this case, the mirror distance equals one wavelength(the peak wavelength of the emission spectrum). In this case theemission is not only determined by the FP microcavity's spacing, butalso is strongly dependent on the position of the active layer withinthe two reflectors, due to the cavity standing wave effect.

FIG. 11 is a schematic representation of a Fabry-Perot (FP) microcavitymode (m=2) that can be achieved in accordance with the presentteachings. FIG. 11 shows that the standing wave's minimum field strengthis at the center of the cavity (at a node).

FIG. 12 is a schematic diagram of a device stack and illustrates alight-emitting layer (EML) at an antinode position of a microcavity asused to enhance light emission in accordance with the present teachings.The stack comprises glass substrate 81, anode 82, HIL 84, one or moreHTM layers 100, HTL 90, EML 94, ETL 96, and cathode 98. The stackgeometry is aligned with a Fabry-Perot microcavity such that EML 94 isin alignment with the antinode of the microcavity and cathode 98 acts ametal reflector. If the light-emitting layer (EML) is positioned at thecenter/node, its emission will be suppressed. On the other hand, if theEML is positioned at the antinode (as shown) where the field strength ofthe standing wave is at a maximum, the emission can be enhanced. Basedon this simple mode and the microcavity spacing d, the EML positionbetween the two reflectors can both strongly affect the optical emissioncharacteristics, including the emission chromaticity and its brightness,and thus define a microcavity effect.

An adjusted hole transport layer (HTL)/hole injection layer (HIL) caneffectively smooth the substrate and affect the emission spectrum,including the microcavity effect, as the HTL thickness varies. Anexample of using a microcavity model to tune the emission spectrum(color) and light emission intensity (brightness) is given in FIG. 13,and Table 1. The Hole Injection Layer II (HIL2) is printed using athermal printing technique and its thickness is varied from 0 nm to 120nm. FIG. 13 is a graph showing blue OLED emission chromaticity as afunction of HIL2 thickness (x nm) in accordance with the presentteachings. As the HIL2 thickness increases, a circular pattern isobserved in its emission spectrum (or CIE coordinates) because theresonant optical mode in the microcavity has moved from the fundamentalmode (m=1) to the second harmonic mode (m=2), as the HIL2 layerthickness increases.

TABLE 1 HIL2 Thickness (nm) CIE-x CIE-y 0 0.134 0.170 15 0.134 0.192 350.135 0.208 65 0.138 0.227 71 0.144 0.207 100 0.143 0.170 110 0.1390.156 120 0.135 0.163

A method of forming a microcavity for an organic light-emitting deviceis provided by the present teachings. The method can comprise anapplying step, an energizing step, a transferring step, and a depositingstep. For example, FIG. 14 is a flow diagram of a method 510 of forminga microcavity for an organic light-emitting device in accordance withthe present teachings. An applying step 520 is shown followed by anenergizing step 530, a transferring step 540, a depositing step 550, anda second depositing step 560. A liquid ink can be applied to a transfersurface for forming a layer of an organic light-emitting device. Theliquid ink can be defined by a carrier fluid and dissolved or suspendedfilm-forming organic material. The transfer surface can be energized tosubstantially evaporate the carrier fluid and form a dry film organicmaterial on the transfer surface. The dry film organic material can betransferred from the transfer surface to a substrate such that the dryfilm organic material is deposited on the substrate in substantially asolid phase. The result is the formation of a first organic bufferlayer. The substrate can comprise a first reflective electrode. Thetransfer surface can be positioned at a distance of from about 1.0 μm toabout 10.0 mm from the substrate during the transferring, for example,at a distance of from about 10.0 μm to about 100.0 μm from thesubstrate. The dry film organic material can be deposited to build up alayer thickness at a rate of from about 0.1 nm/sec to about 500 nm/sec,for example, at a rate of from about 0.1 nm/sec to about 50 nm/sec.

A light-emitting organic material can be deposited over the firstorganic buffer layer to form an emitting layer such that the firstorganic buffer layer is between the substrate and the emitting layer.The light-emitting organic material can emit light at an emissionwavelength. A second reflective electrode can be deposited over theemitting layer such that the emitting layer is between the firstreflective electrode and the second reflective electrode and an OLEDmicrocavity is formed. At least one of the first and second reflectiveelectrodes can be semi-transparent or translucent. The first reflectiveelectrode and the second reflective electrode can be separated from oneanother by a distance. The distance can correspond to a depth of themicrocavity. The depth of the microcavity can be configured forresonance emission of the emission wavelength of the light-emittingorganic material.

A microcavity for an organic light-emitting device is provided by thepresent teachings. The microcavity can comprise a substrate, a dry filmorganic material layer, an emitting layer, and a second reflectiveelectrode. The substrate can comprise a first reflective electrode. Thedry film organic material layer can be formed on the substrate andcomprise a first surface facing the substrate and a second surfaceopposite the first surface. An emitting layer over the dry film organicmaterial layer can be provided such that the dry film organic materiallayer is between the first reflective electrode and the emitting layer.The emitting layer can comprise a light-emitting organic material thatemits light at an emission wavelength. The second reflective electrodeover the emitting layer can be provided such that the emitting layer isbetween the first reflective electrode and the second reflectiveelectrode. The second surface can exhibit a surface roughness of fromabout 0.5 nm to about 1.0 μm as the root mean squared of surfacethickness deviations in an area of 10 μm², for example, from about 1.0nm to about 500 nm, or from about 5.0 nm to about 500 nm. In someembodiments, the area measured is a 10 μm by 10 μm surface. The organiclight-emitting device stack can exhibit a luminosity efficiency of fromabout 1.01 to about 2.0, that is, it can exhibit an increase inluminosity by a factor of from about 1.01 to about 2.0 relative to theluminosity of the same microcavity but with a smooth surface having asurface roughness of less than 5.0 nm expressed as the root mean squareof the surface thickness deviation in an area of 10×10 μm². At least oneof the first and second reflective electrodes can be semi-transparent ortranslucent. The first reflective electrode and the second reflectiveelectrode can be separated from one another by a distance. The distancecan correspond to a depth of the microcavity, and the depth of themicrocavity can be configured for resonance emission of the emissionwavelength of the light-emitting organic material.

Any microcavity or feature of the same can be employed in themicrocavity and method of the present teachings, for example, includingthose described in U.S. Pat. No. 5,405,710, U.S. Pat. No. 6,861,800 B2,U.S. Pat. No. 6,917,159 B2, U.S. Pat. No. 7,023,013 B2, and U.S. Pat.No. 7,247,394 B2; U.S. Patent Application Publications Nos. US2007/0286944 A1 and US 2009/0115706 A1; Huang et al., “ReducingBlueshift of Viewing Angle for Top-emitting Organic Light-EmittingDevices” (2008); Lee et al., “Microcavity Effect of Top-Emission OrganicLight-Emitting Diodes Using Aluminum Cathode and Anode,” Bull. KoreanChem. Soc., 2005, Vol. 26, No. 9; Wu et al., “Microcavity Effects inOrganic Light-Emitting Devices, Chapter 9, pp. 265-292 in OrganicElectronics: Materials, Processing, Devices, and Applications, (So,ed.), CRC Press New York (2010); Bulovic et al., Phys., Rev. B 58: 3730(1998); and Lee et al., Appl. Phys. Lett. 92 (2008) 033303, which areincorporated herein by reference in their entireties.

The microcavity can incorporate one or more quarter wave stacks (QWS). AQWS is a multi-layer stack of alternating high index and low indexdielectric thin-films, each one a quarter wavelength thick. A QWS can betuned to have high reflectance, low transmittance, and low absorptionover a desired range of wavelengths.

The use of a transparent conductive phase-layer is optional. If atransparent conductive phase-layer is used, the combined thickness ofthe transparent conductive phase-layer and an organic EL mediumstructure can be selected to tune the microcavity OLED device to haveresonance at a predetermined wavelength. For example, such predeterminedwavelength can correspond to a center-wavelength of one of red, green,or blue light emitted from the microcavity OLED device constructed inaccordance with the present teachings. The thickness can satisfy thefollowing equation:

2Σn ₁ L _(i)+₂ N _(s) L _(s)+(Q _(m1) +Q _(m2))λ/2π=mλ

wherein n_(i) is the index of refraction and Li is the thickness of theith sublayer in the organic EL medium structure, n_(s) is the index ofrefraction, L_(s) is the thickness, which can be zero, of transparentconductive phase-layer, Q_(m1) and Q_(m2) are the phase shifts inradians at the two organic EL medium structure metal electrodeinterfaces, respectively, λ is the predetermined wavelength to beemitted from the device, and m is a non-negative integer. For ease ofmanufacturing considerations and for color purity, it is preferred tohave m equal to 1 for the blue pixels and equal to 0 or 1 for the greenand red pixels.

The distance between the anode and cathode helps determine themicrocavity resonance wavelength. The resonance wavelength, and moreparticularly, the strength of the resonance, along with the resultingefficiency of the device, also depend on the distance between the EMLand each of the two electrodes. In particular, for optimal deviceperformance, the distance between an electrode and the center point ofthe EML can approximately satisfy the following equation:

2Σn ₁ L _(s) +Q _(m1)λ/2π=m _(D)λ

wherein n_(i) is the index of refraction, L_(i) is the thickness of theith sublayer in the organic EL medium structure, Q_(m1) is the phaseshift in radians at the organic EL medium structure metal cathodeinterface, λ is the predetermined wavelength to be emitted from thedevice, and m_(D) is a non-negative integer.

To help minimize the absorption of light by the light transmissivemetallic electrode, a high index of refraction absorption-reducing layercan be employed between the light transmissive electrode and thesubstrate. The absorption-reducing layer can reduce an electric fieldproduced by a light wave, and absorb the light wave, within the lighttransmissive electrode. To a good approximation, this result can beaccomplished by having the electric field of the light wave reflectedback, from the interface between this absorption-reducing layer and thesubstrate, such that it interferes destructively with, and thus partlycancels, the electric field of the light passing out of the device. Foran absorption-reducing layer having a higher index of refraction thanthe substrate, the following equation can be approximately satisfied:

2n _(A) L _(A) +n _(T) L _(T)=(m _(A)+½)λ

where n_(A) and L_(A) are the index of refraction and the thickness ofabsorption-reducing layer respectively, n_(T) and L_(T) are the realpart of the index of refraction and the thickness of light transmissivemetallic bottom-electrode, respectively, and m_(A) is a non-negativeinteger. The value of m_(A) can be as small as practical, for example,from about 0 to about 2. The beneficial effects of theabsorption-reducing layer are generally higher when higher index ofrefraction materials are used.

The following examples are given to illustrate the nature of the presentinvention. It should be understood, however, that the present inventionis not to be limited to the specific conditions or details set forth inthese examples.

EXAMPLES Example 1

This example demonstrates the functional and superior properties of theOLED components and methods of producing the same, in accordance withthe present teachings. For a 100 nm thick film, 2 drops of ink (about 12picoliters) were applied @ 1.2% ink concentration @ 100 HZ. The loadingtemperature was 150° C. A boil-off temperature of about 250° C. was usedfor a period of from about 200 milliseconds to about 1.0 second. A 250°C.-380° C. temperature ramp was then used for a period of from about 200milliseconds to 800 milliseconds to evaporate the solids. A 350° C.-900°C. clean temperature was then used. The print pitch was about 50 μm. Theas-deposited film looked hazy and the AFM surface roughness greater than5.0 nm. The printed film was subjected to a post-bake at from about 150°C. to about 200° C. for from about 10 seconds to about 5.0 minutes, on ahot plate in a nitrogen environment. Atomic force microscopy (AFM) dataconfirms the surface roughness was reduced to 2 nm or less.

The apparatuses, systems, and methods described herein are exemplary innature, and other materials and structures can be used. Functional OLEDscan be achieved by combining the various layers described in differentways, or layers can be omitted entirely, for considerations such asdesign, performance, and cost factors. Other layers not specificallydescribed can also be included. Materials other than those specificallydescribed can be used. Although many of the exemplary embodimentsprovided herein describe various layers as comprising a single material,it is understood that combinations of materials, such as a mixture ofhost and dopant, or more generally, a mixture, can be used. Also, thelayers can have various sublayers. The names given to the various layersherein are not intended to be strictly limiting. For example, a holetransport layer that transports holes and injects holes into an emissivelayer can be described as a hole transport layer or as a hole injectionlayer or as an HTL/HIL. An OLED can be described as having an “organiclayer” disposed between a cathode and an anode. This organic layer cancomprise a single layer, or can further comprise multiple layers ofdifferent organic materials as described herein.

Materials, systems, and methods not otherwise described can also beused, such as OLEDs comprised of polymeric materials (PLEDs) includingthose described in U.S. Pat. No. 5,247,190, which is incorporated hereinby reference in its entirety. By way of further example, OLEDs having asingle organic layer can be used. OLEDs can be stacked, for example, asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated herein by reference in its entirety. For example, thesubstrate can include an angled reflective surface to improveout-coupling, such as a mesa structure as described in U.S. Pat. No.6,091,195 to Forrest et al., and/or a pit structure as described in U.S.Pat. No. 5,834,893 to Bulovic et al., which are incorporated herein byreference in their entireties.

Although at least one layer is deposited by thermal printing, any layercan instead or additionally be deposited by any suitable method. For theorganic layers, methods can include thermal evaporation methods, inkjetmethods such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196(which are incorporated herein by reference in their entireties),organic vapor phase deposition (OVPD) methods, such as described in U.S.Pat. No. 6,337,102 B1 to Forrest et al. (incorporated herein byreference in its entirety), and organic vapor jet printing (OVJP)methods such as described in U.S. Pat. No. 7,431,968 B1 (incorporatedherein by reference in its entirety). OVPD is a separate and distincttechnique from the thermal printing technique described herein. Othersuitable deposition methods can include spin coating and other solutionbased processes. Solution based processes are preferably carried out innitrogen or other inert atmospheres. For the other layers, other methodsinclude thermal evaporation. Patterning methods that can be used includedeposition through a mask, cold welding such as described in U.S. Pat.Nos. 6,294,398 and 6,468,819 (incorporated herein by reference in theirentireties), and patterning associated with deposition methods such asinkjet and OVJP.

Devices fabricated in accordance with the present teachings can beincorporated into a wide variety of consumer products, such as flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms can be used to control devices fabricated inaccordance with the present teachings, including passive matrix andactive matrix control mechanisms. The apparatuses, methods, and systemsdescribed herein can have applications in devices other than OLEDs.Examples of such other applications include optoelectronic devices suchas organic solar cells and organic photodetectors, as well as organicdevices such as organic transistors.

The utilization of a microcavity in OLEDs in accordance with the presentteachings can provide the following advantages: improving color puritythrough spectrum narrowing, enhancing EML efficiency and brightness, andforming organic lasers. The depth of the microcavity can be adjusted toachieve a laser of desired wavelength. Stimulated emission occurs withinthe microcavity to produce coherent light. An electrode can be providedwith an aperture of desired size and shape to permit a laser beam toexit the microcavity.

While embodiments of the present disclosure have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions will now occur to those skilledin the art without departing from the disclosure. It should beunderstood that various alternatives to the embodiments of thedisclosure described herein can be employed in practicing thedisclosure.

1. A method of forming a microcavity for an organic light-emittingdevice, the method comprising: applying a liquid ink to a transfersurface, the liquid ink defined by a carrier fluid and dissolved orsuspended film-forming organic material for forming a layer of anorganic light-emitting device; energizing the transfer surface tosubstantially evaporate the carrier fluid and form a dry film organicmaterial on the transfer surface; transferring the dry film organicmaterial from the transfer surface to a substrate such that the dry filmorganic material is deposited on the substrate in substantially a solidphase, to form a first organic buffer layer, the substrate comprising afirst reflective electrode, and the dry film organic material beingdeposited to build up a layer thickness at a rate of from about 0.1nm/sec to about 500 nm/sec; depositing a light-emitting organic materialover the first organic buffer layer to form an emitting layer such thatthe first organic buffer layer is between the substrate and the emittinglayer, the light-emitting organic material emitting light, uponexcitation, at a peak emission wavelength; and depositing a secondreflective electrode over the emitting layer such that the emittinglayer is between the first reflective electrode and the secondreflective electrode, to form an OLED microcavity; wherein at least oneof the first and second reflective electrodes is semi-transparent, thefirst reflective electrode and the second reflective electrode areseparated from one another by a distance, the distance corresponds to adepth of the microcavity, and the depth of the microcavity is configuredfor resonance emission of the peak emission wavelength.
 2. The method ofclaim 1, wherein the applying, energizing, and transferring providessimultaneous control of a pattern and thickness of the first organicbuffer layer.
 3. The method of claim 1, wherein the emitting layer isspaced from the first reflective electrode by a first distance andspaced from the second reflective electrode by a second distance, andthe first and second distances are optimized for maximal luminosity ofthe microcavity during operation.
 4. The method of claim 1, wherein thetransferring comprises transferring the dry film organic materialdirectly onto the first reflective electrode.
 5. The method of claim 1,wherein the first organic emitting layer is deposited directly onto thebuffer layer.
 6. The method of claim 1, wherein the first organic bufferlayer comprises at least one of a hole injection layer, a hole transportlayer, an emission layer, an electron transport layer, and an electroninjection layer.
 7. The method of claim 1, further comprising baking,prior to depositing additional layers, the first organic buffer layer ata first bake temperature of from about 50° C. to about 250° C. for afirst bake time of from about 5.0 milliseconds to about 5.0 hours. 8.The method of claim 1, further comprising baking the first organicbuffer layer at a first bake temperature of from about 50° C. to about250° C. for a first bake time of from about 5.0 milliseconds to about5.0 hours to form a first baked organic layer for an organiclight-emitting device.
 9. The method of claim 8, wherein at least one ofthe deposition rate and bake time are adjusted so that the first bakedorganic layer exhibits a rough character.
 10. The method of claim 8,wherein at least one of the deposition rate and bake time are adjustedso that the first baked organic layer exhibits a smooth character. 11.The method of claim 10, wherein at least one of the deposition rate, thebake time, the distance, the concentration of the film-forming organicmaterial in the liquid ink, the temperature of the substrate during thetransferring, and the thickness of the first organic buffer layer areadjusted such that the first baked organic layer has a surface roughnessof from about 0.5 nm to about 10 nm expressed as the root mean square ofthe surface thickness deviation in an area of 10×10 μm².
 12. The methodof claim 10, wherein at least one of the deposition rate, the bake time,the distance, the concentration of the film-forming organic material inthe liquid ink, the temperature of the substrate during thetransferring, and the thickness of the first organic buffer layer areadjusted such that the first baked organic layer has a surface roughnessof less than 5.0 nm expressed as the root mean square of the surfacethickness deviation in an area of 10×10 μm².
 13. The method of claim 8,wherein at least one of the deposition rate, the bake time, thedistance, the concentration of the film-forming organic material in theliquid ink, the temperature of the substrate during the transferring,and the thickness of the first organic buffer layer are adjusted suchthat the first baked organic layer exhibits a porous structure.
 14. Themethod of claim 1, wherein the film-forming organic material exhibits aglass transition temperature range and the method further comprisesbaking the first organic buffer layer at a bake temperature of fromwithin the glass transition temperature range to above the glasstransition temperature range to form a crystalline organic layer havinga conductivity of from about 1.0×10⁻⁹ S/m to about 1.0×10⁻¹ S/m.
 15. Themethod of claim 14, wherein the bake temperature is from about 250° C.to about 450° C. and the first organic buffer layer is heated at thebake temperature for a bake time of from about 5 milliseconds to about5.0 hours
 16. The method of claim 14, wherein the crystalline organiclayer has a crystallinity as measured by an average grain size of fromabout 0.5 nm to about 100 μm.
 17. The method of claim 14, wherein thecrystalline organic layer comprises at least one of a hole injectionlayer, a hole transport layer, an emission layer, an electron transportlayer, and an electron injection layer.
 18. The method of claim 1,further comprising: applying a second liquid ink to a second transfersurface, the second liquid ink defined by a carrier fluid and dissolvedor suspended film-forming organic material for forming a layer of anorganic light-emitting device; energizing the second transfer surface tosubstantially evaporate the carrier fluid and form a second dry filmorganic material on the second transfer surface; and transferring thesecond dry film organic material from the second transfer surface to thefirst organic layer such that the second dry film organic material isdeposited in substantially a solid phase, to form a second organiclayer, wherein the first reflective electrode is semi-transparent andthe first organic buffer layer exhibits a refractive index that isintermediate between a refractive index of the substrate and arefractive index of the second organic layer.
 19. The method of claim18, wherein the refractive index of the substrate is from about 1.01 toabout 1.55 and the refractive index of the second organic layer is fromabout 1.60 to about 5.01.
 20. The method of claim 1, wherein thetransfer surface is positioned at a distance of from about 1.0 μm toabout 10.0 mm from the substrate during the transferring.
 21. The methodof claim 1, wherein the transfer surface is positioned at a distance offrom about 10.0 μm to about 100.0 μm from the substrate during thetransferring.
 22. The method of claim 1, wherein the dry film organicmaterial is deposited to build up a layer thickness at a rate of fromabout 0.1 nm/sec to about 50 nm/sec.
 23. An organic light-emittingdevice OLED microcavity formed by the method of claim
 1. 24. Amicrocavity for an organic light-emitting device, the microcavitycomprising: a substrate comprising a first reflective electrode; a dryfilm organic material layer formed on the substrate and comprising afirst surface facing the substrate and a second surface opposite thefirst surface; an emitting layer over the dry film organic materiallayer such that the dry film organic material layer is between the firstreflective electrode and the emitting layer, the emitting layercomprising a light-emitting organic material that emits light, uponexcitation, at a peak emission wavelength; and a second reflectiveelectrode over the emitting layer such that the emitting layer isbetween the first reflective electrode and the second reflectiveelectrode, wherein the second surface exhibits a surface roughness offrom about 5.0 nm to about 1.0 μm as the root mean squared of surfacethickness deviations in an area 10×10 μm², the organic light-emittingdevice stack exhibits an increase in luminosity by a factor of fromabout 1.01 to about 2.0 relative to the luminosity of the samemicrocavity but with a second surface having surface roughness of lessthan 5.0 nm expressed as the root mean square of the surface thicknessdeviation in an area of 10×10 μm², at least one of the first and secondreflective electrodes is semi-transparent, the first reflectiveelectrode and the second reflective electrode are separated from oneanother by a distance, the distance corresponds to a depth of themicrocavity, and the depth of the microcavity is configured forresonance emission of the peak emission wavelength.
 25. The microcavityof claim 24, wherein the dry film organic material layer comprises fromabout 2 sub-layers to about 20 sub-layers.
 26. The microcavity of claim24, wherein the dry film organic material layer comprises a baked dryfilm organic material layer that has been baked at a temperature of atleast 50° C.